Support extension icons in ScriptCreateDialog

[fuzzybinary]

Attempt to grab the icon for a script type from an extension first, before falling back to the theme.

This adds a method to option_button to allow the ScriptCreateDialog to set the max size of an item icon, so that it can set the size from the Editor Theme when reading the icon from extension.

Example from Godot Dart:

Fixes #98800

[fuzzybinary]

@Ivorforce Updated so that theme takes precedence unless it returns the fallback icon, at which point it will ask the extension.

[Ivorforce]

This is two changes in one (resizable language icon, and asking GDExtensions for language icons); normally I'd put them in two PRs or at least two commits, but I think it's fine here.
Implementation looks good to me!

[KoBeWi]

Any easy way to test this?

[fuzzybinary]

@KoBeWi You can install Godot Dart. Prior to this change it will have the default invalid icon and after it will use the included Dart icon.

[KoBeWi]

You can install Godot Dart.

I don't know how. I'm not familiar with Dart, the downloaded release has no .gdextension file and I tried following the instructions, but ran into problems.

[fuzzybinary]

@KoBeWi See if this helps: https://youtu.be/4VyS9piW_gM (sorry I probably should have linked it in the original comment).

Note, I've also noticed that for some reason the extension sometimes requires an extra reboot after everything is installed. I have no idea why.

If you don't want to install Dart (which you will need to run dart pub get), I guess the other way to do this would be to find any other extension that adds a language, (like Lua maybe?) and modify it's .gdextension file to supply the icon for the type.

[KoBeWi]

Ok I managed to get it working. btw the Actions link in your README points to wrong repo.

[KoBeWi]

I think it's fine, but the changes outside ScriptCreateDialog are unnecessary.

[fuzzybinary]

Removed the unnecessary additions to OptionsButton

[KoBeWi]

Needs to be squashed into 1 commit.

[fuzzybinary]

Done and adjusted the commit comments to be correct.

[akien-mga]

Thanks!