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/inspector_dock.cpp

@@ -530,6 +530,7 @@ InspectorDock::InspectorDock(EditorNode *p_editor, EditorData &p_editor_data) {
 	search->set_h_size_flags(Control::SIZE_EXPAND_FILL);
 	search->set_placeholder(TTR("Filter properties"));
 	search->add_icon_override("right_icon", get_icon("Search", "EditorIcons"));
+	search->set_clear_button_enabled(true);
 	add_child(search);
 
 	warning = memnew(Button);