Add SystemApi USE_UNRESTRICTED_KEEP_CLEAR_AREAS

Normal applications should have restrictions on how big/many keep-clear
areas they can set. This is to prevent malicious apps from misusing the
API and causing unexpected effects (like the Pip moving unexpectedly or
too much around the screen).

System apps, however, can be trusted to set any keep-clear areas.

In this CL we introduce a new permission to allow system apps to set
unrestricted keep-clear areas. We send two lists to Shell - one with
restricted, the other one with unrestricted keep-clear areas. When
moving floating windows away, the Shell can decide to always take into
account unrestricted keep-clear areas and be more restrictive about the
restricted ones.

Bug: 209578131
Bug: 209577354
Test: atest CtsWindowManagerDeviceTestCases:KeepClearRectsTests
Test: atest WindowStateTests
Test: atest DisplayContentTests

Change-Id: I68804c50fb81173b0795cf30dd71ea91abd02229