[TextServer] Improve ligature cursor handling.

Fix mid-grapheme hit test.
Fix OpenType features property handling, add default features override option.
Enable mid-grapheme cursor by default.

scene/gui/line_edit.h

@@ -97,7 +97,7 @@ private:
 	PopupMenu *menu_dir = nullptr;
 	PopupMenu *menu_ctl = nullptr;
 
-	bool caret_mid_grapheme_enabled = false;
+	bool caret_mid_grapheme_enabled = true;
 
 	int caret_column = 0;
 	int scroll_offset = 0;