[DisableTrackpad] Change instances of trackpad to touchpad

To maintain system-wide consistency, we are replacing "trackpad" with
"touchpad" in all variable and file names.

Bug: 372891935
Change-Id: If0dab9ad2d7c96518c4a12d1f379f41a0b385cc1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5922522
Reviewed-by: Akihiro Ota <akihiroota@chromium.org>
Reviewed-by: Katie Dektar <katie@chromium.org>
Commit-Queue: Jesulayomi Kupoluyi <lkupo@google.com>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Reviewed-by: Ahmed Mehfooz <amehfooz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1369563}