Revert "Delete the Touchpad applet"

This reverts commit 3b402664.

Removing the applet entirely was too heavy-handed, as it can serve a
valid purpose as a status notifier to remind people who have manually
disabled their touchpads that they have done so.

BUG: 445095
FIXED-IN: 5.23.4
(cherry picked from commit 4d03ce00)