Update WM Jetpack impl to use WindowMetrics

Before, SettingsExtensionImpl#getWindowLayoutInfo returned empty window
info when Activity was not attached. Now, it returns the correct info
after Activity create.

Test: atest CtsWindowManagerJetpackTestCases:ExtensionTest
Fixes: 152534741
Fixes: 155121604
Fixes: 155692339
Change-Id: Ieded3b70ff14aba03581bf7501cc5e923b5eed33