Missing required extension files or directories currently result in
opaque "Directory not found" errors being logged during the update index
phase. This can be frustrating to those developing extensions. Add some
context so folks know where to start looking.

Release Notes:

- N/A

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Co-authored-by: Kirill Bulatov <mail4score@gmail.com>
Co-authored-by: Kirill Bulatov <kirill@zed.dev>