Do not check if hidden if hidden files are allowed

[vidartf]

Description

Currently, even if allow_hidden is set to true, we still call the potentially expensive check for each and every file. The clauses in the conditional should be switched so that it short-circuits on the setting.

Reproduce

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4. See error '...'

Expected behavior

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[vidartf]

Also, does the async file manager not need to await the is_hidden calls?

[kevin-bates]

Also, does the async file manager not need to await the is_hidden calls?

There are two is_hidden methods in play here. One takes two parameters and is a synchronous library function from jupyter_core, and the other is a class method defined on the respective contents manager classes, with AsyncFileContentsManager's is_hidden() being async. It looks like the references in AFCM are to the library function.

Frankly, I don't think AFCM's is_hidden, dir_exists, and file_exists don't need to exist (and I suspect there may be others like that). If these were to be removed, the handlers will also need to be updated since they currently ensure_async on these.