Add Quick Open dialog

This dialog searches every Resource-derived file in the project, making
it extremely useful for searching everything from audio files to scripts.

Unlike the Quick Open Script and Quick Open Scene dialogs, you don't need
to think about the type of file you're opening, just its name.

Shift + Alt + O was chosen to match the existing shortcuts for
Quick Open Scene and Quick Open Script.

editor/editor_node.cpp

@@ -1921,6 +1921,12 @@ void EditorNode::_menu_option_confirm(int p_option, bool p_confirmed) {
 			file->set_title(p_option == FILE_OPEN_SCENE ? TTR("Open Scene") : TTR("Open Base Scene"));
 			file->popup_centered_ratio();
 
+		} break;
+		case FILE_QUICK_OPEN: {
+
+			quick_open->popup_dialog("Resource", true);
+			quick_open->set_title(TTR("Quick Open..."));
+
 		} break;
 		case FILE_QUICK_OPEN_SCENE: {
 
@@ -5694,6 +5700,7 @@ EditorNode::EditorNode() {
 	p->add_separator();
 	p->add_submenu_item(TTR("Open Recent"), "RecentScenes", FILE_OPEN_RECENT);
 	p->add_separator();
+	p->add_shortcut(ED_SHORTCUT("editor/quick_open", TTR("Quick Open..."), KEY_MASK_SHIFT + KEY_MASK_ALT + KEY_O), FILE_QUICK_OPEN);
 	p->add_shortcut(ED_SHORTCUT("editor/quick_open_scene", TTR("Quick Open Scene..."), KEY_MASK_SHIFT + KEY_MASK_CMD + KEY_O), FILE_QUICK_OPEN_SCENE);
 	p->add_shortcut(ED_SHORTCUT("editor/quick_open_script", TTR("Quick Open Script..."), KEY_MASK_ALT + KEY_MASK_CMD + KEY_O), FILE_QUICK_OPEN_SCRIPT);
 	p->add_separator();

editor/editor_node.h

@@ -146,6 +146,7 @@ private:
 		FILE_SAVE_OPTIMIZED,
 		FILE_OPEN_RECENT,
 		FILE_OPEN_OLD_SCENE,
+		FILE_QUICK_OPEN,
 		FILE_QUICK_OPEN_SCENE,
 		FILE_QUICK_OPEN_SCRIPT,
 		FILE_OPEN_PREV,