phabricator: add custom vcr matcher to match request bodies
Currently when the phabricator extension's conduit output changes the tests
don't notice since the default vcr matcher only matches on 'method' and 'uri',
not the body.
Add a custom matcher that checks the same params are in the body (ignoring
vcr's in-built body matcher can't be used since it fails under py3 with a
"UnicodeEncodeError" on the "€ in commit message" tests.
The DREV ids have decreased since the recordings were generated against a
different phabricator instance to avoid spamming mercurial-devel.
Differential Revision: https://phab.mercurial-scm.org/D6347