Make touch handles appear after long tap selection in a Textfield.

CL:4701865 hides the touch handles after a long press gesture, so that
they are not visible during long press drag selection. However, I forgot
to make the touch handles show again after a long tap. (This wasn't
caught by the LongPressSelection test since the event generator
currently generates an extra Tap event after releasing the touch.)

Fix this error and adjust the test.

Bug: b:244116654
Change-Id: I85dfbf9047dab1ff0e4a7875e0904a8d4272e5cf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4772855
Reviewed-by: Thomas Lukaszewicz <tluk@chromium.org>
Commit-Queue: Michelle Chen <michellegc@google.com>
Cr-Commit-Position: refs/heads/main@{#1182947}