Release Context#isUiContext(Context)

The purpose of this API is to verify whether a context is an
UI context or not. We can also leverage the jetpack WindowManager
to all kinds of UI contexts v.s. Activities only currently by
release this API.

Bug: 170275820
Test: atest ContextIsUiContextTest
Change-Id: I334b63e555331e46d0a94ec9f721bd675f1ab331