commitctx: extract copy information encoding into extra into commit.py The encoding of copy information into extra has multiple subcases and become quite complicated (eg: empty list can be explicitly or implicitly stored for example). In addition, it is niche experimental feature since as it affect the hash, it is only suitable for user who don't mercurial for storage server side (ie: Google). Having this complexity part of the changelog will get in the way of further cleanup. We could have to either move more of that logic into the changelog or to move or extract more of the logic at the higher level. We take the second approach and start gather logic in dedicated function in commit.py.

commitctx: create the new extra dict on its own line A trivial move to make the next changeset easier to read.

commitctx: explicitly pass `manifest` to _commit_manifest As pointed out by Yuya Nishihara.

phabricator: unconditionally pop `test_vcr` to fix debugcallconduit 11592ce6a711 / D8525 accidentally broke debugcallconduit in non-test scenarios because it stopped popping `test_vcr` from `kwargs` unconditionally, so when `--test-vcr` isn't set the empty string still gets passed down as the value of `test_vcr` in `kwargs`. However unlike all the other commands debugcallconduit doesn't have an `**opts` argument to receive it, so it aborts because of invalid arguments. Differential Revision: https://phab.mercurial-scm.org/D8852