Add clear text button to LineEdit

- Add pressed state to clear button
- Enable clear button on all inputs with search icon
- Remove duplicate clear buttons
- Fix rendering of icon for center and right alignments
- Add clear button to more search fields
- Add clear icon to default theme
- Add method to control enabled state of clear button
- Add property to enable clear button from inspector

editor/plugins/script_editor_plugin.cpp

@@ -219,6 +219,9 @@ void ScriptEditorQuickOpen::_notification(int p_what) {
 		case NOTIFICATION_ENTER_TREE: {
 
 			connect("confirmed", this, "_confirmed");
+
+			search_box->add_icon_override("right_icon", get_icon("Search", "EditorIcons"));
+			search_box->set_clear_button_enabled(true);
 		} break;
 	}
 }