Use constexpr in VelocityTracker

Previously, defining DEBUG_STRATEGY as 1 would fail to compile.

In this patch, the defines are changed to bools, in order to fix this
going forward.

Also, when I was porting the velocitytracker algorithm to python, I
realized that one of the velocities was wrong. I updated the value. I
didn't check other values, though. It was previously passing likely
because the tolerance for velocity is quite large.

Bug: 192439431
Test: atest libinput_tests
Change-Id: I70b44af6cd5567ee8321b29e509c628fa0b4950e