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/project_settings_editor.h

@@ -69,7 +69,6 @@ class ProjectSettingsEditor : public AcceptDialog {
 	HBoxContainer *search_bar;
 	Button *search_button;
 	LineEdit *search_box;
-	ToolButton *clear_button;
 
 	HBoxContainer *add_prop_bar;
 	AcceptDialog *message;
@@ -158,7 +157,6 @@ class ProjectSettingsEditor : public AcceptDialog {
 	void _translation_filter_mode_changed(int p_mode);
 
 	void _toggle_search_bar(bool p_pressed);
-	void _clear_search_box();
 
 	void _copy_to_platform_about_to_show();