mouse-panel: Remove "Test Settings" from header

Initial implementation to move the "Test Settings" button from the header to the AdwPreferencesPage of the mouse panel.

Remove "Test Settings" from the header

Add "Test Settings" to mouse-panel ui

@felipeborges Let me know if any changes are to be made since this will require approval from the design team.

(Need to be updated) Screenshots attached: https://gitlab.gnome.org/Atbrat/changes_screengrabs/-/tree/main/gnome-control-center-grabs

See #2839 (closed)

(Updated) Changes in action:

Changesmouserlatest.mp4