rust-narrow: fix loop that never loops This was caught by `clippy`. I guess the narrow tests leave something to be desired, since this previously only checked the first valid pattern.

dirstate: enforce holding the lock while doing any changes This seems like a sensible sanity check. This already caught the issue in largefile. This will catch more issue when we start using similar context manager for operation other than the parent changes.

largefile: make sure we hold the lock when updating the second dirstate The largefile extension uses a second dirstate file (and object) to track some states. In some situations, it is lazily updated when needed. These operations might not have the lock taken. This means they might conflict and race with other ongoing operations. So we now take the lock to do these operations. This was caught by the next commit.

dirstate: rename `@requires_no_parents_change` too This match the rename of the context manager.

dirstate: rename `@requires_parents_change` to `@requires_changing_parents` This match the rename of the context manager.

dirstate: write dirstate on successful exit of changing_parents context This is the first step toward having more sensible and predicatable write patterns for the dirstate. Having better write/rollback patterns will greatly reduce and clarify the needs to backup the dirstate.

dirstate: rename parentchange to changing_parents Since the new argument breaks the API anyway, we can rename it to a better name. The previous name `parentchange` might be seen as something active, a function that would directly change the parents, however this is just a context manager to frame the operation that will change the parents and adjust the dirstate content accordingly. In addition, the future sister method that will be about changes to tracking and files would have a hard time fitting in the same naming scheme in a clear way. The new naming uses a clear prefix will make it more distinct from other dirstate methods and easier to extend with other similar contexts.

dirstate: pass the repo to the `changeparent` method If we want the context to be responsible for writing (and we want it), we need to have access to a localrepository object. So we now requires a localrepository object as an argument to this context manager.

dirstate: warn about non-explicitly rolledback parent-change Now that the invalidation is dealt with by the context manager itself, we should no longer need this in the unlocking code. We start with issuing a warning if this is the case before actually dropping this code later.

dirstate: invalidate changes when parent-change fails When an error occurs during changing parents, we should invalidate all dirstate modifications and reload the dirstate. This is currently done by a `unlock` callback on the `wlock`. To fix this anomaly, we start dealing with the error directly in the context manager and its potential nesting. The "hard" part is to make sure that, when the parent-change context are nested, we and higher level nesting do not continue to use the invalidated dirstate. We introduce dedicated code to enforce that.