[stdlib] cleanup: Remove redundant operator overloads for

String/StringLiteral args

The functionality of each of the removed methods is fulfilled by the
remaining `StringSlice`-taking methods.

For example, we don't need all three of:

	String.__iadd__(StringLiteral)
	String.__iadd__(String)
	String.__iadd__(StringSlice)

StringLiteral and String can both implicitly coerce to StringSlice, so
any callers currently calling one of those two overloads will gracefully
fallback to simply calling the StringSlice-taking overload.

MODULAR_ORIG_COMMIT_REV_ID: 24e87313c0d5a0df8764d98cb8828d32c0ee1a6a

stdlib/src/collections/string/inline_string.mojo

@@ -103,22 +103,6 @@ struct InlineString(Sized, Stringable, CollectionElement, CollectionElementNew):
     # Operator dunders
     # ===------------------------------------------------------------------=== #
 
-    fn __iadd__(mut self, literal: StringLiteral):
-        """Appends another string to this string.
-
-        Args:
-            literal: The string to append.
-        """
-        self.__iadd__(StringSlice(literal))
-
-    fn __iadd__(mut self, string: String):
-        """Appends another string to this string.
-
-        Args:
-            string: The string to append.
-        """
-        self.__iadd__(string.as_string_slice())
-
     fn __iadd__(mut self, str_slice: StringSlice):
         """Appends another string to this string.
 
@@ -158,21 +142,7 @@ struct InlineString(Sized, Stringable, CollectionElement, CollectionElementNew):
             buffer.append(0)  # Add the NUL byte
             self._storage = Self.Layout(String(buffer^))
 
-    fn __add__(self, other: StringLiteral) -> Self:
-        """Construct a string by appending another string at the end of this string.
-
-        Args:
-            other: The string to append.
-
-        Returns:
-            A new string containing the concatenation of `self` and `other`.
-        """
-
-        var string = self
-        string += StringSlice(other)
-        return string
-
-    fn __add__(self, other: String) -> Self:
+    fn __add__(self, other: StringSlice) -> Self:
         """Construct a string by appending another string at the end of this string.
 
         Args:
@@ -183,8 +153,8 @@ struct InlineString(Sized, Stringable, CollectionElement, CollectionElementNew):
         """
 
         var string = self
-        string += other.as_string_slice()
-        return string
+        string += other
+        return string^
 
     fn __add__(self, other: InlineString) -> Self:
         """Construct a string by appending another string at the end of this string.
@@ -378,22 +348,6 @@ struct _FixedString[CAP: Int](
     # Operator dunders
     # ===------------------------------------------------------------------=== #
 
-    fn __iadd__(mut self, literal: StringLiteral) raises:
-        """Appends another string to this string.
-
-        Args:
-            literal: The string to append.
-        """
-        self.__iadd__(literal.as_string_slice())
-
-    fn __iadd__(mut self, string: String) raises:
-        """Appends another string to this string.
-
-        Args:
-            string: The string to append.
-        """
-        self.__iadd__(string.as_string_slice())
-
     @always_inline
     fn __iadd__(mut self, str_slice: StringSlice) raises:
         """Appends another string to this string.

stdlib/src/collections/string/string.mojo

@@ -1145,30 +1145,6 @@ struct String(
             ptr[sum_len] = 0
         return Self(buffer^)
 
-    @always_inline
-    fn __add__(self, other: String) -> String:
-        """Creates a string by appending another string at the end.
-
-        Args:
-            other: The string to append.
-
-        Returns:
-            The new constructed string.
-        """
-        return Self._add[True](self.as_bytes(), other.as_bytes())
-
-    @always_inline
-    fn __add__(self, other: StringLiteral) -> String:
-        """Creates a string by appending a string literal at the end.
-
-        Args:
-            other: The string literal to append.
-
-        Returns:
-            The new constructed string.
-        """
-        return Self._add[False](self.as_bytes(), other.as_bytes())
-
     @always_inline
     fn __add__(self, other: StringSlice) -> String:
         """Creates a string by appending a string slice at the end.
@@ -1181,30 +1157,6 @@ struct String(
         """
         return Self._add[False](self.as_bytes(), other.as_bytes())
 
-    @always_inline
-    fn __radd__(self, other: String) -> String:
-        """Creates a string by prepending another string to the start.
-
-        Args:
-            other: The string to prepend.
-
-        Returns:
-            The new constructed string.
-        """
-        return Self._add[True](other.as_bytes(), self.as_bytes())
-
-    @always_inline
-    fn __radd__(self, other: StringLiteral) -> String:
-        """Creates a string by prepending another string literal to the start.
-
-        Args:
-            other: The string to prepend.
-
-        Returns:
-            The new constructed string.
-        """
-        return Self._add[True](other.as_bytes(), self.as_bytes())
-
     @always_inline
     fn __radd__(self, other: StringSlice) -> String:
         """Creates a string by prepending another string slice to the start.
@@ -1237,24 +1189,6 @@ struct String(
         if not has_null:
             s_ptr[sum_len] = 0
 
-    @always_inline
-    fn __iadd__(mut self, other: String):
-        """Appends another string to this string.
-
-        Args:
-            other: The string to append.
-        """
-        self._iadd[True](other.as_bytes())
-
-    @always_inline
-    fn __iadd__(mut self, other: StringLiteral):
-        """Appends another string literal to this string.
-
-        Args:
-            other: The string to append.
-        """
-        self._iadd[False](other.as_bytes())
-
     @always_inline
     fn __iadd__(mut self, other: StringSlice):
         """Appends another string slice to this string.

stdlib/src/collections/string/string_slice.mojo

@@ -540,30 +540,6 @@ struct StringSlice[mut: Bool, //, origin: Origin[mut]](
             return True
         return memcmp(s_ptr, rhs_ptr, s_len) == 0
 
-    @always_inline
-    fn __eq__(self, rhs: String) -> Bool:
-        """Verify if a `StringSlice` is equal to a string.
-
-        Args:
-            rhs: The `String` to compare against.
-
-        Returns:
-            If the `StringSlice` is equal to the input in length and contents.
-        """
-        return self == rhs.as_string_slice()
-
-    @always_inline
-    fn __eq__(self, rhs: StringLiteral) -> Bool:
-        """Verify if a `StringSlice` is equal to a literal.
-
-        Args:
-            rhs: The `StringLiteral` to compare against.
-
-        Returns:
-            If the `StringSlice` is equal to the input in length and contents.
-        """
-        return self == rhs.as_string_slice()
-
     fn __ne__(self, rhs_same: Self) -> Bool:
         """Verify if a `StringSlice` is not equal to another `StringSlice` with
         the same origin.
@@ -591,32 +567,6 @@ struct StringSlice[mut: Bool, //, origin: Origin[mut]](
         """
         return not self == rhs
 
-    @always_inline
-    fn __ne__(self, rhs: String) -> Bool:
-        """Verify if span is not equal to another `StringSlice`.
-
-        Args:
-            rhs: The `StringSlice` to compare against.
-
-        Returns:
-            If the `StringSlice` is not equal to the input in length and
-            contents.
-        """
-        return not self == rhs
-
-    @always_inline
-    fn __ne__(self, rhs: StringLiteral) -> Bool:
-        """Verify if span is not equal to a `StringLiteral`.
-
-        Args:
-            rhs: The `StringLiteral` to compare against.
-
-        Returns:
-            If the `StringSlice` is not equal to the input in length and
-            contents.
-        """
-        return not self == rhs
-
     @always_inline
     fn __lt__(self, rhs: StringSlice) -> Bool:
         """Verify if the `StringSlice` bytes are strictly less than the input in