Add method to setDefaultMouseDisplay in ChoreographerTest

This CL adds setDefaultMouseDisplayId method to the
PointerChoreographerTest base class.
This will allow us to customize this in the next CL.

Test: atest inputflinger_tests
Bug: 245989146
Flag: EXEMPT TEST_ONLY
Change-Id: Ieea0f252b21fc0eb3002201feb36bdb2bb546488