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 <span class="ref-name">mouse-a11y</span> in 6 minutes and 41 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Build
passed #199297
build

00:03:26

 
  Test
passed #199299
asan

00:03:14

passed #199298
test

00:00:43

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