shared/icon-label: Prevent moc from being appended to global file

[gxalpha]

Description

Like described in 5eb04cd (#11101), this prevents the moc_icon-label.cpp from being included in the global mocs_compilation.cpp file. Looks a bit ridiculous to create a new file for this, but that's just because content-wise icon-label is only a header.

Motivation and Context

Oversight from #11148 due to the fact that there was no .cpp file where this include would usually go.

How Has This Been Tested?

macOS 15
Looked at mocs_compilation.cpp, confirmed that <P4W7YBUBWD/moc_icon-label.cpp> was included previously but no longer is.

Types of changes

• Tweak (non-breaking change to improve existing functionality)

• Code cleanup (non-breaking change which makes code smaller or more readable)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[PatTheMav]

While the change itself looks correct, I'm unsure whether it's a worthwhile change as it's mainly a cosmetic change.

If icon-label is to be a "header-only" library, then it is correct to make all its function implementations inline (which has become the only meaning of the keyword, mainly to disable the one-definition-rule for the marked functions and variables).

Obviously header-only Qt objects will then incur the compile-time cost of needing their moc-ed code be included globally in the project.

If that is to be fixed, the entire class should be converted into a "non-header" library, its functions moved into the compilation unit and the header converted to its original purpose as a description of the class memory layout.

[gxalpha]

This makes sense. I moved the setter functions into the newly created file.

[RytoEX]

I imagine that these files should now be named the same as the class that is defined.

[PatTheMav]

One could argue that it could keep the current name for consistency with the other elements in the shared directory, but as its contents would be updated to the new design rules established for the frontend directory anyway, it wouldn't hurt to go with the program for all additions.

[gxalpha]

Updated the PR to rename the file(s). Left the directory names as-is.