Improve the pygments lexer to cover GDScript 2 better

[Qubus0]

we've recently updated the gdscript lexer for our own documentation, this is a port of those changes to fit the godot docs

please check as many pages as you can for errors i might have missed.

also let me know if the colors are fine like this. i think some of the existing colors may be from an older theme and not quite up to date, but i didn't touch them for now.

main changes are functions having proper blue color now, global functions being purple, all classes getting the correct greens (including builtins and types having the different green), and proper colors for $String, string names and node paths

[Qubus0]

Side by side screenshot

[Calinou]

Tested locally, it works as expected. Both dark and light theme seem to work.

This is a great start, as it now looks much closer to the Godot script editor (which is the intended goal).

[Qubus0]

Name and Punctuation didn't have css classes yet. adding them makes the () and = bluish, pretty hard to notice, and fixes code in warning callouts being yellow

[Calinou]

Looks great now!

Dark	Light

I can confirm the code color in admonitions is fixed now.

[Qubus0]

singulars done, squashed everything, should be ready - let me know if anything else stands out to you

[Qubus0]

okay, realized most of the light theme colors were outdated, so i brought everything closer to the editor theme. including the yellowed background which the editor doesn't have (improves clarity imo, might split some opinions though)

before	after

[Qubus0]

Updated preview

dark	light
note the function declaration colors above are fixed but	everything below still has the wrong ones but i didn't want to redo everything

[Qubus0]

fixed member vars color and ...args

dark	light

code not changed, just added for simpler screenshot