merge: default into stable for release candidate

debugdiscovery: include the number of heads in all sets We already displayed information about heads of the common set that are either local or remote heads. We now also do so for heads of the common set that are both local and remote heads too. This is useful because various step in the set discovery algorithm have head specific optimizations.

recover: add a --[no-]verify flag For trivial cases, the cost of the verify run after `hg recover` is getting in the way. In addition for very large repositories, the cost is simply too high to be paid, making `hg recover` an unusable commands. We introduce a --verify flag, set by default. If is automatically associated with a --no-verify flag that one can use to skip the verify step. We might consider changing the default behavior in the future. However this is out of scope for this series.

bundle2: handle compression in _forwardchunks _forwardchunks is used to compensate for getbundle protocol deficits. Since it transparently decodes the payload, it also needs to remove the corresponding compression parameter in case the server decides to send one. This the wire protocol part of issue 5990. Differential Revision: https://phab.mercurial-scm.org/D6182

changelog: parse copy metadata if available in extras This lets read back the copy metadata we just started writing. There are still many places left to teach about getting the copy information from the changeset, but we have enough ({file_copies}, specifically) that we can add it now and have some test coverage of it. Differential Revision: https://phab.mercurial-scm.org/D6186

copies: add config option for writing copy metadata to file and/or changset This introduces a config option that lets you choose to write copy metadata to the changeset extras instead of to filelog. There's also an option to write it to both places. I imagine that may possibly be useful when transitioning an existing repo. The copy metadata is stored as two fields in extras: one for copies since p1 and one for copies since p2. I may need to add more information later in order to make copy tracing faster. Specifically, I'm thinking out recording which files were added or removed so that copies._chaincopies() doesn't have to look at the manifest for that. But that would just be an optimization and that can be added once we know if it's necessary. I have also considered saving space by using replacing the destination file path by an index into the "files" list, but that can also be changed later (but before the feature is ready to release). Differential Revision: https://phab.mercurial-scm.org/D6183

revsetbenchmark: add some simpler revset for heads and roots This revset might leverage compiled code in the future so lets start to track them.

repoview: flag `server.view` as experimental Ideally, the non-experimental version of `experimental.extra-filter-revs` will cover the use case for `server.view=immutable` well enough than having to have this dedicated configuration. Since `server.view` is not part of any release, I would prefer to have it marked as experimental to avoid having it to support it for ever.

repoview: move subsettable in a dedicated module The dictionary got moved in `branchmap` to avoid import cycle. However, we are about to needs it in repoview too. So we introduce a now module to define that that mapping.

upgrade: support upgrade to/from zstd storage (issue6088) Now that we have an official config option for a shiny format improvement, we better make it simple to migrate to/from it.