phabricator: update hgmatcher to cope with the new data format
The new conduit format can't be matched by the existing matcher since it shifts
all the data into an urlencoded string of JSON, the order of which isn't stable
between runs. Instead detect JSON values of params and load them into python
dicts, which python will then naturally deep-equal compare.
Differential Revision: https://phab.mercurial-scm.org/D7055