largefiles: remove the first `changing_parents` in `updatelfiles` Now that the `update_file` call have been migrated, we can drop the semantically-wrong `changing_parents` context.

largefiles: use `hacky_extension_update_file` in `updatelfiles` This is what the function is meant for.

largefiles: use `hacky_extension_update_file` in `synclfdirstate` This is what the function is meant for.

largefiles: use `hacky_extension_update_file` in `openlfdirstate` This is what the function is meant for.

win32text: make the hacky call cover more cases Now that I understand what this is doing, It seems like the case for `p1_tracked` were covered by neither the code nor the test. Now the code cover it at least.

win32text: drop the `changing_parents` context in revert upgrade We are not changing parents here, so let us not pretend we do.

win32text: clean up and clarify the post-revert hack of dirstate The change is unrelated to changing parents and should not be a in a "changing_parents" context. This call is quite hacky, but now it is at least explicitly hacky. We will drop the `changing_parents` context in the next changesets, but we kept this change simple to help readability.

dirstate: introduce a `hacky_extension_update_file` method See inline documentation for details.

mq: properly take the wlock during the full qfold operation Otherwise the operation could be raced… for unknown result.

locking: hold the wlock for the full duration of the "keyword demo" The risk of racing the demo is low, since it seems to create its own repository on the fly. However it is clearer and more consistent.