Upstream check/set flag rules to ShellTestCase

- So that each test doesn't need to include them to use
  @EnableFlags/@DisableFlags/@RequiresFlagsDisabled/
  @RequiresFlagsEnabled/etc

Bug: 378565144
Test: atest WMShellUnitTests
Flag: EXEMPT bugfix
Change-Id: Id51c82abc01f2da1a3cf6887e43b26906981e844