Add Intrsumentation#resetInTouchMode for instrumenting

As IWindowManager#setInTouchMode(boolean) will override the global touch
mode state for testing usage, it would be nice to add an API for
restoring the original default touch mode state after the test.

Bug: 220180252
Bug: 220907843
Test: m checkapi
Change-Id: I60909e7da5be3158e2630848f2b6b4b213fc3a01