Add Ctrl + L / Cmd + Shift + G shortcut to focus path bar in FileDialog

This also tweaks EditorFileDialog to use the same shortcut,
while making it select the path text after focusing
(like in most file managers).

Ctrl + L / Cmd + Shift + G can also now be used to focus on the
property name in the project settings editor, as well in the
Input Map, Autoload, Shader Globals and Global Groups tabs.

editor/action_map_editor.cpp

@@ -380,6 +380,10 @@ LineEdit *ActionMapEditor::get_search_box() const {
 	return action_list_search;
 }
 
+LineEdit *ActionMapEditor::get_path_box() const {
+	return add_edit;
+}
+
 InputEventConfigurationDialog *ActionMapEditor::get_configuration_dialog() {
 	return event_config_dialog;
 }