Add support for macOS

[MichaelJBerk]

This PR adds support for OpenLauncher on macOS. Currently the launcher builds and runs on macOS, but can't download new releases or launch the game.

• OpenLauncher now uses the correct binary name on macOS so that it can launch the executable properly.
• On all platforms, OpenLauncher currently uses ZipFile.ExtractToDirectory to extract the release once it's been downloaded. However, this method will not preserve file aliases on macOS, and since OpenRCT2.app contains several of them, the extracted application won't launch. To fix this, this PR calls/usr/bin/ditto in a subprocess to extract the .zip, which will preserve the files properly.
• Since OpenLoco isn't currently supported on macOS, it doesn't appear in the launcher.
• .gitignore is updated to ignore .ds_store and other hidden files that macOS likes to make

[IntelOrca]

Currently the CI does not build or publish a macOS version, are you able to add this? Without it, no macOS version will be released.

[MichaelJBerk]

I added a macOS build to the CI action, though it needs to use scripts to build/package it, since the process is a bit more complicated for macOS (it needs to build both x64 and arm64 versions, combine them, and then build the proper .app structure for them). The action doesn't sign and notarize the app, since I'm not entirely sure of the best way to handle that for CI.

[AaronVanGeffen]

Builds fine locally using build-mac.sh with .NET 9.0. Packages fine into a bundle using package-mac.sh. The resulting launcher runs fine, downloads and runs releases as well:

Looks like the CI job needs work, though? I'd try restarting it, but it seems I don't have the required rights for the OpenLauncher repository.

[AaronVanGeffen]

That call to codesign seems to have done the trick. I don't quite understand how (what key is being used?) but it launches: