Implement BlurHash placeholders for image preview with VFS

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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](https://github.com/nextcloud/server/issues/40676) available from the server via https://github.com/nextcloud/server/pull/41044
This will allow for displaying image preview placeholders on [Windows](https://github.com/nextcloud/desktop/issues/3407) and [MacOS](https://github.com/nextcloud/desktop/issues/4335) instantly and therefor improve user experience when browsing files.

example: