Write --xattrs metadata as macOS Spotlight metadata (rev 2)

[ghost]

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Modified the line of my previous #29184 about checking the availability of plistlib.dumps (from sys.version_info to hasattr().) Everything else unchanged.

Resolves #2545, resolves #8089, resolves #28945.

On macOS, it is preferable to write --xattrs metadata as Spotlight metadata so that they are shown in Finder's Get Info window and searchable by Spotlight/Finder.

These metadata will be written to Spotlight metadata: webpage_url, title, description and uploader.
Other metadata, upload_date and format, are written to dublin core as before since there seem to be no corresponding Spotlight metadata.

Uses standard plistlib on Python 3.4+, PyObjC module if available, or plutil command.
Tries to find Apple's xattr command which can set binary data if xattr module is not available.
PyObjC is usually pre-installed for Python 2.7 on macOS and can be installed with pip (pyobjc-framework-Cocoa is enough). plutil and xattr commands are usually pre-installed on macOS.

[porg]

Hi, I'm the one who proposed #8089 and am glad that someone made a code contribution for this!

Can you please explain how you mapped?

• For upload_date and format I also provide what I think are the corresponding Spotlight metadata fields
• All integrated into the following table:

xattr	Spotlight Metadata Attribute
user.dublincore.contributor ("uploader" in Youtube terminology)	kMDItemContributors
user.dublincore.date	kMDItemContentCreationDate and/or simply the Creation Date via filesystem calls
user.dublincore.description	kMDItemDescription
user.dublincore.format	kMDItemFinderComment (plain text , user editable in Finder) or kMDItemCodecs (parse and map against proper identifiers which is certainly more complex or maybe even impossible)
user.dublincore.title	kMDItemTitle
user.xdg.referrer.url	kMDItemWhereFroms

Could you please provide a build of this?

• Compatible with an Intel Mac on macOS 11 Big Sur so that I can test and report?
• I installed yt-dlp via brew, so I should have all the latest dependencies.
• I'm just not that git-savvy atm, don't know so well how to download (merge?) and build myself.