Readability improvements to PointerChoreographer_tests

In PointerChoreographer_tests, we make assertions on the lifecycle of
the PointerControllers that Choreographer creates, to make sure it is
releasing resources appropriately.

Rather than holding the  PointerControllers as a list of
weak_ptrs in the test code, store the created PointerControllers
directly on the stack in the test so that it is easy to make assertions
on it to improve readability. We can also make assertions that the
Chorographer has released all its references by ensuring that the
refrence held by the test code is the one and only reference.

Bug: 293587049
Test: atest inputflinger_tests
Change-Id: I31872f6f6e991178ef6dc550ee8ea7d8be7d9f92