sae_j1850_vpw: update for API v3, adjust to recent requirements

IRC user pman92 reported that this decoder exists, and started migration
to the v3 API. This commit completes the migration, and adds missing
decoder infrastructure which has become mandatory recently.

Adjust the boilerplate: Drop FSF postal address. No Python output, add
category tag, unambiguous annotation class and row names. Add reset()
method. Use common code for edge detection.

This commit also addresses minor style nits. Pass the most recent
pulse's edges as ss and es to the data bit handling routine. Adjust
whitespace to unbreak editor navigation and to improve readability.

Use a more verbose name for the decoder, "vpw" appears a little short
and collision happy, and is not found when users search for "j1850".

[ Indentation changed, see whitespace ignoring diff for the essence. ]

Reported-By: pman92 <redacted>