DolphinQt: Add page table fastmem to JIT menu

This can be useful for experimenting with how a game behaves with and
without page table fastmem. As with everything in the JIT menu, this is
only available if Dolphin's debugger is enabled.

I didn't add this in 989a95a when I added the setting itself because we
were under a string freeze for Dolphin 2603a at the time.

Source/Core/DolphinQt/MenuBar.h

@@ -288,6 +288,7 @@ private:
   QAction* m_jit_block_linking;
   QAction* m_jit_disable_cache;
   QAction* m_jit_disable_fastmem;
+  QAction* m_jit_disable_page_table_fastmem;
   QAction* m_jit_disable_fastmem_arena;
   QAction* m_jit_disable_large_entry_points_map;
   QAction* m_jit_clear_cache;