branch: make --force work even when specifying revs The `hg branch` command accepts a `--force` parameter that allows to "set branch name even if it shadows an existing branch". However, before this patch, that didn’t work when specifying revs with `-r`.

tests: use new, use-case-specific methods from merge module Differential Revision: https://phab.mercurial-scm.org/D8169

merge: introduce a merge() for that use-case In the same vein as some earlier patches like f546d2170b0f (merge: introduce a clean_update() for that use-case, 2020-01-15). Differential Revision: https://phab.mercurial-scm.org/D8168

merge: drop redundant mergeforce argument from hg.merge() The only caller that passed a value for either `force` or `mergeforce` passed the same value for both, so let's simplify the interface by accepting only `force`. Differential Revision: https://phab.mercurial-scm.org/D8167

merge: change default of hg.merge()'s "force" argument from None to False The argument is only passed to `mergemode.update()`, and that function treats `None` just like `False`, so `False` seems clearer. Differential Revision: https://phab.mercurial-scm.org/D8166

debugmergestate: make templated Our IntelliJ team wants to be able to read the merge state in order to help the user resolve merge conflicts. They had so far been reading file contents from p1() and p2() and their merge base. That is not ideal for several reasons (merge base is not necessarily the "graft base", renames are not handled, commands like `hg update -m` is not handled). It will get especially bad as of my D7827. This patch makes the output s a templated. I haven't bothered to make it complete (e.g. merge driver states are not handled), but it's probably good enough as a start. I've done a web search for "debugmergestate" and I can't find any indication that any tools currently rely on its output. If it turns out that we get bug reports for it once this is released, I won't object to backing this patch out on the stable branch (and then perhaps replace it by a separate command, or put it behind a new flag). The changes in test-backout.t are interesting, in particular this: ``` - other path: foo (node not stored in v1 format) + other path: (node foo) ``` I wonder if that means that we actually read v1 format incorrectly. That seems to be an old format that was switched away from in 2014, so it doesn't matter now anyway. Differential Revision: https://phab.mercurial-scm.org/D8120