[net7] Make use of App Thinning for fat applications

[spouliot]

ref: https://developer.apple.com/documentation/xcode/reducing-your-app-s-size

Assemblies (.dll) and the associated .aotdata* files should be removable from the final (as downloaded) app bundle after Apple post-process them.

A fat app will have several files that are architecture-specific, e.g. armv7 and arm64 being common (even if declining) for iOS apps. Only one of them is required at execution time (on device) based on the CPU of the target device. Apple already makes some modifications for apps (e.g. the main native executable is thinned) but .net specific formats are not known (by default).

Directories / Files	Legacy	net6 rc.1	diff	%
System.Private.CoreLib.aotdata.arm64	0	731,992	731,992	-
System.Private.CoreLib.aotdata.armv7	0	683,728	683,728	-
System.Runtime.aotdata.arm64	0	504	504	-
System.Runtime.aotdata.armv7	0	504	504	-
Xamarin.iOS.aotdata.arm64	0	48,328	48,328	-
Xamarin.iOS.aotdata.armv7	0	48,512	48,512	-
.//.xamarin/ios-arm
System.Private.CoreLib.dll	0	765,440	765,440	-
System.Runtime.dll	0	5,120	5,120	-
Xamarin.iOS.dll	0	73,728	73,728	-
.//.xamarin/ios-arm64
System.Private.CoreLib.dll	0	775,680	775,680	-
System.Runtime.dll	0	5,120	5,120	-
Xamarin.iOS.dll	0	73,728	73,728	-

Notes

• This could be tested inside the submissions tests, see "Automate the Generation of the App Size Report" in https://developer.apple.com/documentation/xcode/reducing-your-app-s-size

• It's unknown if (it would be recent) App thinning is used for macOS (App store downloads only) but it could become a "thing" at anytime since it makes sense with Intel/arm64 fat binaries.

[rolfbjarne]

This will not be done in the .NET 7 time frame due to time constraints, so moving to .NET 8.

[rolfbjarne]

This won't be an issue in .NET 8, because we're dropping support for 32-bit iOS (#15216).