uart: Convert to PD API version 3

uart: Convert to PD API version 3

Adjust the UART protocol decoder, to make use of the query based API.
Have edges detected and unrelated samples skipped by common code.

This implementation keeps some redundancy in place (like checking for
having reached specific sample numbers, while the backend managed that
for us). This approach reduces the diff and shall simplify review.

Only some common checks in decode() were moved to the start of the
routine, outside of the sample inspection loop.