mouse: Don't use a separate box for touchpad switch

The Touchpad section looks like a single listbox
so let's handle it that way too.

This eliminates an unnecessary split in the touchpad
section that is noticeable when navigating with a keyboard.
11 jobs for mouse-a11y in 6 minutes and 41 seconds (queued for 4 seconds)
Status Name Job ID Coverage
  Build
passed build #199297

00:03:26

 
  Test
passed asan #199299

00:03:14

passed test #199298

00:00:43

 
  Manual
manual armv8 #199304
allowed to fail manual
manual flatpak #199300
allowed to fail manual
manual msan #199303
allowed to fail manual
manual ppc64le #199305
allowed to fail manual
manual tsan #199301
allowed to fail manual
manual ubsan #199302
allowed to fail manual
 
  Review
manual review #199306
allowed to fail manual
manual stop_review #199307
allowed to fail manual