Improve conflict handling in macOS Virtual Files module Sync Engine

[claucambra]

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Feature description

The macOS VFS sync engine will currently handle conflicts in very naive ways. For example, incoming file-name clashes will lead to the new file being ignored. Similarly, with files that have changed both locally and on the server, the file provider sync engine will always choose to push the local changes

We should more gracefully detect these conflicts and allow the user to resolve the issue by creating actionable conflict files (and maybe a conflict dialog)