Merge compat fake focus properties into one

Merge PROPERTY_COMPAT_FAKE_FOCUS_OPT_IN/OUT properties into PROPERTY_COMPAT_ENABLE_FAKE_FOCUS and move to WindowManager class to be consistent with other existing properties in WindowManager and also in anticipation of us making those public APIs in Android U.

Fix: 263987615
Test: atest WmTests:LetterboxUiControllerTest
atest WmTests:LetterboxConfigurationTest
atest WmTests:SizeCompatTests#testShouldSendFakeFocus_compatFakeFocusEnabled
atest WmTests:SizeCompatTests#testShouldSendFakeFocus_compatFakeFocusDisabled

Change-Id: Ic10b3a25e3a8bcef25be27b549148d36a2192fbc