LibGUI: Add TabWidget::activate_last_tab()

Author: https://github.com/iCristalrope
Commit: 1b7850f511
Pull-request: https://github.com/SerenityOS/serenity/pull/13080
Reviewed-by: https://github.com/awesomekling

Userland/Libraries/LibGUI/TabWidget.h

@@ -66,6 +66,7 @@ public:
 
     void activate_next_tab();
     void activate_previous_tab();
+    void activate_last_tab();
 
     void set_text_alignment(Gfx::TextAlignment alignment) { m_text_alignment = alignment; }
     Gfx::TextAlignment text_alignment() const { return m_text_alignment; }