Add WindowContext support to WindowLayoutComponentImpl

To make activity embedding library able to listen to folding state
change consistently, we should add WindowContext support to
WindowLayoutComponentImpl, which only supported Activity previously.

This CL can also benefit VoiceInteractionSession support on
WindowLayoutComponent.

Bug: 207494880
Bug: 204073440
Test: use in follow-up CL and report folding state change successfully

Change-Id: I7a4fea6ed00b52996c7cffb33aadb934abe811c8