phonewm: fix allapp tests for phone & improve stem key testing infra

- Create the testing infra StemKeyGestureTests paralleling to
  PowerKeyGuesureTests.
- Restrict Stem Primary behavior fields' visbilities.
- Fix the all app tests that are broken for phone.

Test: atest StemKeyGestureTests
BUG: 281047310
Merged-In: If7782804ed7ab1edf9926382e22f307cb644a95e
Change-Id: If7782804ed7ab1edf9926382e22f307cb644a95e
(cherry picked from commit f7d58ed5)