These frames are used for computing the legacy insets which won't be
used anymore. We should only maintain the new insets system now.
This CL also unhides Rect#inset APIs.
Bug: 149813814
Test: atest WindowFrameTests DisplayPolicyLayoutTests InsetsPolicyTest
SplashscreenTests ManifestLayoutTests WindowMetricsTests
WindowInsetsAnimationImeTests WindowInsetsControllerTests
WindowUntrustedTouchTest DisplayContentTests
Change-Id: I06e40be6342b2ae35f7cc3e6f4ebdbe68edf0499
b73471b4ec