bundle2-push: introduce a list of part generating functions Instead of explicitly calling a few function to generate part in the bundle, we now have a list of all part generators. This should make it easier for extensions to adds new part in the bundle. This new way to extend the push deprecates the old `_pushbundle2extraparts` way.

bundle2-push: move changegroup push validation inside _pushb2ctx When bundle2 push includes more than just changesets, we may have no changegroup to push yet still have other data to push. So we now try to performs a bundle2 push in all cases. The check for changegroup inclusion is moved into the ``_pushb2ctx`` function in charge of creating the changegroup part. The bundle2 part is aborted if no actual payload part have been added to the bundle2.

push: use `stepsdone` to control changegroup push through bundle10 or bundle20 We use the newly introduced `pushop.stepsdone` attribute to inform older methods than changegroup have already been pushed using a newer method.

push: add a ``pushop.stepsdone`` attribute This attribute will record what steps were performed during the bundle2 push. This will control whenever the old way push must be performed or skipped. This will ultimately be used by changegroup, phases, obsmarkers, bookmarks and any other kind of data ones may want to exchange even when bundle2 support is missing.

bundle2: add a ``bundle20.nbparts`` property This property can be used to know how much parts have been added to the bundle2. This will be useful to check if any part have been generated for a push.

bundle2-push: extract changegroup logic in its own function We extract the creation of changegroup related parts into its own function. This precludes the inclusion of more diverse data during the bundle2 push. We use a closure to carry the logic that need to be perform when processing the server reply.

bundle2: call _pushbundle2extraparts a bit sooner This is the first step of a refactoring that will ease the inclusion of new part in the bundle2 push and includes more information (like phases) in this push We need to move the function a bit sooner to be able to group the generation of `b2x:check:heads` and `b2x:changegroup` part in an external function. We move it sooner to preserve parts creation order bundle2 tests rely on. At the ends of this refactoring the `_pushbundle2extraparts` will be replaced by another mechanism anyway.

templatekw: add 'subrepos' keyword to show updated subrepositories 'subrepos' template keyword newly added by this patch shows updated subrepositories. For the compatibility with the list of subrepositories shown in the editor at commit: - 'subrepos' is empty, at revisions removing '.hgsub' itself - 'subrepos' is calculated between the revision and the first parent of it, at merge revisions To avoid silent regression, this patch also confirms "hg diff" of ".hgsubstate" and parents for each target revisions in the test.

templatekw: add 'currentbookmark' keyword to show current bookmark easily Before this patch, complicated template expression below is required to show current active bookmark if it is associated with the changeset. "{bookmarks % '{ifeq(bookmark, current, \"{bookmark}\")}'}" This patch add 'currentbookmark' keyword to show current bookmark easily.

context: extend efficient manifest filtering to when all paths are files On a repository with over 250,000 files and 700,000 commits, this improves cases like hg status --rev <rev> -- <file> # rev is not . from 2.1 seconds to 1.4 seconds. There is further scope for improvement here: for a single file or a small set of files, it is probably more efficient to use filelog linkrevs when possible. However there will always be cases where that will fail (multiple commits pointing to the same file revision, removed files...), so this is independently useful.