Add TestApi to reset locked modifier state

To make CTS tests more reliable, we need a way to clear locked
modifier state that can creep in from other tests since locked
modifier state is global and saved across devices.

Test: atest CtsInputTestCases
Bug: 377353219
Flag: EXEMPT test_only
Change-Id: I8ae29652067966019d18e5f104925b4fbae91408