Fix stashed PiP so it only moves up/down if outside of insets

Add unit tests for adjust() method in PhonePipKeepClearAlgorithm.
This covers test cases for applying gravity, moving PiP away from
keep clear areas (which is equivalent to findUnoccludedPosition test
cases), and for ignoring keep clear areas if PiP is stashed, testing
only the up/down movement added by this change.

Bug: 286478425
Test: atest PhonePipKeepClearAlgorithmTest
Test: before http://recall/-/ekEuGtt9d9HWqkUtAzpHx8/dY9IMjhv5eBf0501pUCPKp
Test: after http://recall/-/ekEuGtt9d9HWqkUtAzpHx8/eLrBdqzAKlGiNvFetdIsh9

Change-Id: I478d364a31652f6507d2a289295d336b62d0db81