phabricator: record all local commits used to create a Differential revision Arcanist records all of the commits that it squashes into a single review, and that info will be helpful when adding similar functionality. This info is used when submitting an updated review, so that the extension can recalculate the old diff and see if a new one is necessary, or if it is just a property update. It also shows on the `commits` tab in the `Revision Contents` section. When submitting in the usual 1:1 commit to review mode, the wire protocol is unchanged. The content of `hg:meta` is a bit odd, but such is the problem when folding several commits. The choice for the parent node is obvious, but the `node` value uses the tip commit because that seems more natural, and is used elsewhere to look up the previous diff when updating. The rest of the attributes follow from there. Differential Revision: https://phab.mercurial-scm.org/D8308