Recent macOS and M1 processor: Prompts to download Rosetta

[willend]

When installing on a fresh installation of macOS on M1/Silicon, the system will detect the McCode.app as being an "Intel" app and request download of Rosetta.

Internally, the app ensures use of an Arm Python etc., so there is no performance hit. But we should prepare for a future without Intel support.

[willend]

It seems that by

1. Adding

    <key>LSArchitecturePriority</key>
    <array>
        <string>arm64</string>
    </array>

(as suggested via https://stackoverflow.com/questions/68199148/application-reports-different-architecture-depending-on-launch-method)

2. Signing the app

The app is finally considered "arm64" on Silicon