Debugger: Fix some theming issues

[chaoticgd]

Description of Changes

The PR addresses the following theming issues:

• The layout switcher tabs appearing in the wrong place for the Windows Vista and Windows 11 styles.
• A weird underline appearing under the non-selected tabs when using the Fusion style on Windows.
• The background colour of the menu bar being wrong when using the Windows Vista style.
• The bottom border of menu bar items being drawn too high.
• The lock/unlock toggle having white on white text when the Windows 11 style is used.
• The KDDockWidgets tab bars not updating when the style changes.

In addition, the custom menu bar has been extracted into its own class and a highlight has been added to the current tab when the Fusion style is used.

This does not fix the position of the layout switcher when using the native macOS theme. I don't have a Mac, so I can't really play with it properly.

This should be merged after #12447 so I can rebase it and update the VS filters file. Done.

Screenshots:

Rationale behind Changes

Fix visual bugs introduced by my docking PR.

Suggested Testing Steps

Try all the different themes on Windows and Linux.