Support script global resource name in EditorFileSystem

* Works for binary and text files.
* Makes EditorQuickOpen work with custom resources again.
* Information is cached and easily accessible.

Properly fixes #66179. Supersedes #66215 and supersedes #62417

**WARNING**: This required breaking backwards binary compatibility (.res and .scn files). Files saved after this PR is merged will no longer open in any earlier versions of Godot.

modules/gdscript/gdscript.h

@@ -228,6 +228,7 @@ public:
 	virtual bool can_instantiate() const override;
 
 	virtual Ref<Script> get_base_script() const override;
+	virtual StringName get_global_name() const override;
 
 	virtual StringName get_instance_base_type() const override; // this may not work in all scripts, will return empty if so
 	virtual ScriptInstance *instance_create(Object *p_this) override;