Move encoder distance per pulse out of the HAL

[calcmogul]

It being there has made adding unit support to the encoder class as-is, as well as writing new encoder classes with unit support, much more painful than it should be.

My ill-fated C++ attempt: #3709
@SamCarlberg tried a Java version and ran into the same issue.

The fundamental issue is distance per pulse doesn't belong in the encoder class/HAL API. It should be a separate thing handled on the subsystem level to convert from sensor units (e.g., radians) to what the user cares about (e.g., distance).