Ability to turn off _CompileAppManifest for library projects

[KirillOsenkov]

We are seeing library projects targeting net6.0-macos where the target _CompileAppManifest and related targets run:

xamarin-macios/msbuild/Xamarin.Shared/Xamarin.Shared.targets

Line 501 in 82482ed

<!-- This target has no inputs, because it must still be run if there are no input app manifests, to set default values -->

I know it's not a lot of overhead, but my understanding that if we know the libraries definitely have nothing to do with MacOS perhaps we should be able to turn off this machinery?

Perhaps AppManifestDetectionEnabled should be respected in a condition in these targets?

See related:
#13583

I think most of these targets don't need to run for regular projects and we should be able to turn them off?

[KirillOsenkov]

On the other hand, perhaps we should be targeting net6.0 instead of net6.0-macos in our library projects??

[KirillOsenkov]

confirmed we need to target net6.0-macos because we use Cocoa APIs from libraries

[rolfbjarne]

Yeah, we could look into adding a property that disables app manifest logic for library projects.

[rolfbjarne]

This will be fixed with the fix for #19028 (whenever we get to do that).