Poke user activity when showing the global actions menu.

Since the power key is always consumed before queueing, and thus doesn't
ever contribute to user activity, we should just always poke user
activity when global actions is triggered to give the user time to
interact with it.

Bug: 31274295
Test: N/A
Change-Id: I9dd00726209c9a425bb2f105d1582eb5326a354c