mergestate: replace `addmergedother()` with generic `addcommitinfo()` (API)
Storing that a file is resolved for the other parent while merging is just one
case of things we will like to store in the mergestate. There are more which we
will like to store.
This patch replaces `addmergedother()` with a much more generic
`addcommitinfo()`. Doing this, we also blinding stores the same key value pair
generated by the merge code instead of touching them.
Differential Revision: https://phab.mercurial-scm.org/D8923
$ hg init repo
$ cd repo
$ touch foo
$ hg ci -Am 'add foo'
adding foo
$ hg up -C null
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
this should be stored as a delta against rev 0
$ echo foo bar baz > foo
$ hg ci -Am 'add foo again'
adding foo
created new head
$ hg debugindex foo
rev linkrev nodeid p1 p2
0 0 b80de5d13875 000000000000 000000000000
1 1 0376abec49b8 000000000000 000000000000
$ cd ..