Implement BlurHash placeholders for image preview with VFS

[PhilippSchlesinger]

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Feature description

Make use of BlurHash (https://blurha.sh/, BlurHash is a compact representation of a placeholder for an image) in Nextcloud Client
using metadata available from the server via nextcloud/server#41044
This will allow for displaying image preview placeholders on Windows and MacOS instantly and therefor improve user experience when browsing files.

example: