InputTracer: Ensure 0 coordinate values are traced, with unit test

The axis bits in PointerCoords are not set when
the value is 0, since that's the default value.

Make sure the coordinate values are always traced
for pointer events, and add unit tests.

Bug: 245989146
Flag: EXEMPT tracing only
Test: Presubmit
Change-Id: I7c291ef56e025e771c382354e10d6b7dda7a8fa4