Add shorthand for using singleton string names

[KoBeWi]

Follow-up to #80573

This PR adds CoreStringName() and SceneStringName() macros as a shorthand for CoreStringNames::get_singleton()-> and SceneStringNames::get_singleton()->. It makes the singleton string names easier to use and code is cleaner.

I also applied some minor cleanup:

• removed some stringname singleton includes from header files
• removed unused stringnames: ___pdcdata, __getvar
• renamed some stringnames to be less confusing (they used underscore for member, but not for string, e.g. _script for "script"

For the last point I had to make some exceptions, because the actual name conflicted with a C++ keyword. I changed the name from _name to name_ (up to discussion), to make it more clear that underscore is not part of the name.

My plan after that is to replace all usage of "strings" and SNAME("strings") with their singleton equivalent if it exists already. Right now they are used inconsistently.

Another thing is that some names are used only once. I think they can be replaced with SNAME(); it didn't exist when they were created.

Production edit: closes godotengine/godot-roadmap#3

[Calinou]

Tested locally, it mostly works as expected.

This reduces binary size by about 8 KB too (optimized Linux x86_64 editor).

106,980,384  godot.linuxbsd.editor.x86_64  <-- This PR
106,988,576  godot.linuxbsd.editor.x86_64.master

However, I get a series of errors when exiting the editor. This occurs on any project, even an empty project:

ERROR: Attempt to disconnect a nonexistent connection from '@CreateDialog@5292:<CreateDialog#505883418985>'. Signal: 'confirmed', callable: 'CreateDialog::_confirmed'.
   at: _disconnect (./core/object/object.cpp:1416)
ERROR: Attempt to disconnect a nonexistent connection from '@CreateDialog@10229:<CreateDialog#775476516600>'. Signal: 'confirmed', callable: 'CreateDialog::_confirmed'.
   at: _disconnect (./core/object/object.cpp:1416)
ERROR: Attempt to disconnect a nonexistent connection from '@CreateDialog@6763:<CreateDialog#575894745070>'. Signal: 'confirmed', callable: 'CreateDialog::_confirmed'.
   at: _disconnect (./core/object/object.cpp:1416)
ERROR: Attempt to disconnect a nonexistent connection from '@CreateDialog@6344:<CreateDialog#556684831719>'. Signal: 'confirmed', callable: 'CreateDialog::_confirmed'.
   at: _disconnect (./core/object/object.cpp:1416)
ERROR: Attempt to disconnect a nonexistent connection from '@CreateDialog@6197:<CreateDialog#550175271553>'. Signal: 'confirmed', callable: 'CreateDialog::_confirmed'.
   at: _disconnect (./core/object/object.cpp:1416)
ERROR: Attempt to disconnect a nonexistent connection from '@EditorFileSystem@3:<EditorFileSystem#28269610226>'. Signal: 'filesystem_changed', callable: 'EditorDirDialog::reload'.
   at: _disconnect (./core/object/object.cpp:1416)
ERROR: Attempt to disconnect a nonexistent connection from '@CreateDialog@4543:<CreateDialog#471121025568>'. Signal: 'confirmed', callable: 'CreateDialog::_confirmed'.
   at: _disconnect (./core/object/object.cpp:1416)
ERROR: Attempt to disconnect a nonexistent connection from '@CreateDialog@4361:<CreateDialog#462698862674>'. Signal: 'confirmed', callable: 'CreateDialog::_confirmed'.
   at: _disconnect (./core/object/object.cpp:1416)

[KoBeWi]

I can't reproduce the errors. Are you sure they are caused by this PR? Any chance for their stack trace?

[akien-mga]

I like the change, and it seems to work fine on my end from a quick test.

Would be good if @Calinou could test again and see if he reproduces the error about missing signal connections.

[Calinou]

Tested locally (rebased on top of master bdc0316), it works as expected now. I can't reproduce the errors on exit anymore.

[akien-mga]

Thanks!

[AThousandShips]

Introduced a conflict with:

• Fix a performance regression when duplicating a node #91329

Writing up a fix