Keep screen on when user undims it manually

When user manually undims the screen x times - it's a clear indication
that they want to keep it on and dimming is not wanted. For such case,
keep the screen on temporarily by acquiring a wakelock,
without changing the actual timeout setting.

Bug: 162367114
Bug: 162422938
Test: atest ScreenUndimDetectorTest
Change-Id: Ib80b569fc9d230d8f77e0baec67c17a3e90be516