Use modules_enabled.gen.h to improve inter dependency checks

- Fix build with gdscript module disabled. Fixes #31011.
- Remove unused `gdscript` compile option.
- Fix build with regex module disabled.
- Fix ImageLoaderSVG to forward declare thirdparty structs.

modules/freetype/SCsub

@@ -102,5 +102,3 @@ if env['builtin_freetype']:
 
 # Godot source files
 env_freetype.add_source_files(env.modules_sources, "*.cpp")
-# Used in scene/, needs to be in main env
-env.Append(CPPDEFINES=['FREETYPE_ENABLED'])