Refactor ProjectSetting overrides

* Overrides no longer happen for set/get.
* They must be checked with a new function: `ProjectSettings::get_setting_with_override()`.
* GLOBAL_DEF/GLOBAL_GET updated to use this

This change solves many problems:
* General confusion about getting the actual or overriden setting.
* Feature tags available after settings are loaded were being ignored, they are now considered.
* Hacks required for the Project Settings editor to work.

Fixes #64100. Fixes #64014. Fixes #61908.

main/main.cpp

@@ -1385,7 +1385,6 @@ Error Main::setup(const char *execpath, int argc, char *argv[], bool p_second_ph
 #ifdef TOOLS_ENABLED
 	if (editor) {
 		packed_data->set_disabled(true);
-		globals->set_disable_feature_overrides(true);
 		Engine::get_singleton()->set_editor_hint(true);
 		main_args.push_back("--editor");
 		if (!init_windowed) {