apple: replace "com.flyinghead.Flycast" by "io.github.flyinghead.flycast"

[scribam]

As mentioned in flathub/org.flycast.Flycast#201, using the reverse-dns name io.github.flyinghead.flycast would be more future-proof 🙂

[flyinghead]

Isn't this going to change the application id for iOS (${MACOSX_BUNDLE_GUI_IDENTIFIER})?
This isn't so much of an an issue for macOS but it is for iOS, since the app is published in AltStore and already installed on some users' devices.
I did publish an app on the AppStore in the past using com.flyinghead.xxx and there's no need to own the domain.

[scribam]

Yes, it will change the application id and... it is probably not a good idea indeed for the current users who already have the application installed.
Since there is no need to own the domain as you say, let's not break anything and close this PR 😅
Thanks for the feedback 🙂