call update_exports from LSP didSave function

exports in the inspector were not properly appearing when a gdscript was saved using an external IDE
this commit adds a call to GDScript::UpdateExports toward the end of GDScriptTextDocument::didSave

modules/gdscript/language_server/gdscript_text_document.cpp

@@ -107,6 +107,7 @@ void GDScriptTextDocument::didSave(const Variant &p_param) {
 		} else {
 			scr->reload(true);
 		}
+		scr->update_exports();
 		ScriptEditor::get_singleton()->update_docs_from_script(scr);
 	}
 }