LibGUI+GMLPlayground: Replace text using ReplaceAllTextCommand

Author: https://github.com/SimonFJ20 🔰
Commit: 661e7d691e
Pull-request: https://github.com/SerenityOS/serenity/pull/13633
Issue: https://github.com/SerenityOS/serenity/issues/11810
Reviewed-by: https://github.com/awesomekling

Userland/Libraries/LibGUI/TextEditor.h

@@ -123,6 +123,7 @@ public:
     TextRange normalized_selection() const { return m_selection.normalized(); }
 
     void insert_at_cursor_or_replace_selection(StringView);
+    void replace_all_text_while_keeping_undo_stack(StringView text);
     bool write_to_file(String const& path);
     bool write_to_file(Core::File&);
     bool has_selection() const { return m_selection.is_valid(); }