pull: merge bookmark updates and imports We do all the things in one go now, updating existing bookmark, adding new ones, and overwriting the ones explicitly specified for --bookmark. This impacts the tests by removing some duplicated or unnecessary output.

pull: gather explicit bookmark pulls with bookmark updates There is no reason to make them at different times. So we gather them. This is the first step toward merging them.

subrepo: stop pulling bookmark manually Bookmark pulling is now done with all the other pull steps in the `exchange.pull` function.

pull: retrieve bookmarks through bundle2 We can retrieve any pushkey namespace through bundle2. So we also ask for bookmark data and use them to update the local repo.

pull: retrieve bookmarks before obsmarkers Retrieving bookmarks before obsmarkers will avoid turning some changesets hidden right before making them visible again if a bookmark keeps them visible.

pull: move bookmark pulling into its own function This requires adding an attribute on the pulloperation object. The bookmark pulling is protected behind a "todostep" as other steps of pull.