We can't process a common-fx.ignore file for a given framework if that
framework isn't included in any of the platforms we're building for.
Example: we can't process common-AppKit.ignore when only iOS is enabled,
because none of the errors listed in common-AppKit.ignore will be reported for
an iOS build.
* Pass any native references to the LinkNativeCode task so that they're linked
with the main executable.
* Copy frameworks and dynamic libraries to the app bundle (also add support for
MSBuild metadata - the CopyToAppBundle property - to avoid copying a framework
/ dynamic library to the app bundle).
* Add tests.
Fixes https://github.com/xamarin/xamarin-macios/issues/11061.
Refactor the Optimizations class to have no conditionally compiled code, which makes
it re-usable from our dotnet-linker code.
Also return any errors or warnings instead of showing/throwing them, which makes
the caller able to show them using whatever means is easiest for the caller.
One test needed an update to the list of valid optimizations, because we now have
a per-platform map of valid optimizations, instead of just a iOS/tvOS/watchOS vs
macOS split ('remove-unsupported-il-for-bitcode' is only valid for watchOS, and now
we say so, while we previously said it was a valid optimization for iOS and tvOS
as well, even though we'd warn about it and do nothing if you tried to set it).
Rolf Bjarne Kvinge