largefiles: rely on main scoping for writing dirstate in `mergeupdate` Yeah, cleaner code.

largefiles: rely on the higher level `changing_giles` in `mergerecordupdates` Now that context open on the main dirstate also affect the underlying one, we can skip opening our own in `mergerecordupdates`

dirstate: use wlock and `dirstate.change_files` to scope the change in `mq` This is the way.

subrepo: use `changing_files` context in subrepository code This is better, not ideal, but better.

subrepo: let black expand some call on multiple lines early newer version of black are righfully doing this, so I apply it before more semantic change to reduce noise in the next changeset.

dirstate: use `dirstate.change_files` to scope the change in `import` This is the way.

dirstate: use `dirstate.change_files` to scope the change in `automv` This is... mostly... the way.

dirstate: use `dirstate.change_files` to scope the change in `amend` This is the way.

dirstate: use the `changing_files` context in the `keyword` demo This is the way.

dirstate: wrap repository change in appropriate context in `test-context` We need the `wlock` (to add files), the `lock` (to commit), a `transaction` (to commit) and a `changing_files` context (to add files). Strictly speaking, we could let the commit take the `lock` and create a `transaction`, but it seems more consistent that way.