os/mac: prefer newest Xcode when searching using mdfind

[carlocab]

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We're currently returning the first match for com.apple.dt.Xcode,
which could be any version if a user has multiple installed.

Instead, let's try to find the newest if all our results have an
Info.plist that we can interrogate for the version.

Maybe resolves #18736?

For reference, on my system, before this change:

❯ brew ruby -e 'puts MacOS.app_with_bundle_id("com.apple.dt.Xcode")'
/Applications/Xcode-14.3.1.app

after this change:

❯ brew ruby -e 'puts MacOS.app_with_bundle_id("com.apple.dt.Xcode")'
/Applications/Xcode.app

[MikeMcQuaid]

Nice, people have complained about this a lot for ages. Looks good as-is but may want a tweak for readability and/or correctness.