Meta: Add a macOS bundle to gn build for ladybird

[ADKaster]

This adds an app bundle to the gn build for ladybird. It includes all the libraries, dependent apps and resource files.

One can now open the ladybird.app app bundle on macOS, use Xcode tools like Instruments on the applications in the app bundle, and even install the app bundle into /Applications :^)

As I asked on the gn mailing list, there's no real "nice" way to currently bundle all the dependent libraries without listing them twice. Perhaps @nico will have a simpler solution :^)

https://groups.google.com/a/chromium.org/g/gn-dev/c/qU5xchay4OE