Report bounds instead of size in WindowMetrics

Use case: Jetpack WM will use them to get the location of windows on
screen and compute the display feature positions in window coordinate
space.

Bug: 150908045
Test: atest FrameworksCoreTests:WindowMetricsTest
Test: atest CtsWindowManagerDeviceTestCases:WindowMetricsTests
Change-Id: Ia08950cd5df35971408e8b17bb27d97d29d0ab9b
Exempt-From-Owner-Approval: API change