Prepare for moving editor and classref translations to godot-editor-l10n repo

- Separate editor interface and property translations.
- Add property translation in TranslationServer.
- The split and merge of the POT/PO/Makefiles and extract scripts is done
  directly in godot-editor-l10n, the files will be removed in the next commit.
- Remove the hardcoded "to_include" lists from the SCsub, we'll only commit the
  files which are ready to inclue.

editor/editor_settings.cpp

@@ -922,6 +922,7 @@ void EditorSettings::setup_language() {
 	}
 	// Load editor translation for configured/detected locale.
 	load_editor_translations(lang);
+	load_property_translations(lang);
 
 	// Load class reference translation.
 	load_doc_translations(lang);