Yoast/AlternativeFunctions: rename sniff, bug fix for fixer, support modern PHP and other improvements

[jrfnl]

Yoast/AlternativeFunctions: minor documentation improvements

Yoast/AlternativeFunctions: safeguard handling of PHP 7.3+ function calls with trailing commas

As of PHP 7.3, the parameter list for a function call can have a trailing comma.

This is already handled correctly by the sniff. This commit just adjusts some pre-existing tests to safeguard this for the future.

Yoast/AlternativeFunctions: add test with PHP 8.0+ nullsafe object operator

... to safeguard that the sniff does not recognize method calls prefixed with the nullsafe object operator as calls to the global functions.

Note: this is already handled by the WPCS parent sniff, this test just safeguards it.

Yoast/AlternativeFunctions: bug fix - fixer could create parse error

If the original function call was already fully qualified in a namespaced file, the fixer would add a superfluous extra namespace separator - \\WPSEO_Utils::format_json_encode(), effectively creating a parse error in the resulting file.

As fully qualified calls to global functions in namespaced files are now the norm in the Yoast repos, this is a clear bug which should be prevented.

Fixed now by removing a potential leading namespace separator before doing the replacement.

Includes additional tests.

Yoast/AlternativeFunctions: bug fix - allow for PHP 5.6+ parameter unpacking

When a function call uses parameter unpacking, the exact parameter count is undetermined, so the auto-fixer should not kick in.

The sniff did not take this into account. Fixed now.

Includes tests.

Yoast/AlternativeFunctions: rename the sniff to JsonEncodeAlternative

... in anticipation of adding support for PHP 8.0+ function calls using named parameters. Supporting this would too complex if there is an open ended possibility of detection of additional function groups being added to this sniff.

The renamed sniff will only handle the [wp_]json_encode() function call detection and replacement.

If in the future additional functions would have Yoast specific alternative and need sniffs, this should be handled by a separate sniff/separate sniffs.

Yoast/JsonEncodeAlternative: refactor the sniff to support PHP 8.0+ function calls with named parameters

PHP 8.0 added support for parameter labels in function calls.

This has two significant consequences for this sniff:

1. We can no longer rely on the parameter count to determine whether the function call can be auto-fixed.
   Instead we need to specifically check for the $value parameter having been passed and no other parameters being passed.
2. For the auto-fixer, we can no longer just swop out the function call for its replacement. We also need to check if the passed parameter was a named parameter and if so, we may need to fix the parameter name as well.

This commit refactors the sniff to take both the above into account.

The refactor also removes some flexibility from the sniff, as, now the sniff has been renamed and will only check for the [wp_]json_encode() function calls, we no longer need to take the potential of additional function groups being checked via this sniff into account.

Includes tests.

Yoast/JsonEncodeAlternative: handle PHP 8.1+ first class callables

PHP 8.1 added support for "first class callables".

As the number of parameters which will be passed to the callable is unknown, the sniff should flag these functions when used as first class callable, but should not auto-fix.

Includes tests.

[coveralls]

coverage: 98.519% (+0.03%) from 98.493%
when pulling 0501528 on JRF/yoastcs-alternativefunctions-various-improvements
into 218d9a2 on develop.