Resolves#14285
1. Make sure `libextension-dotnet.a` gets built, and with the `-DEXTENSION` flag.
2. Make sure `libextension-dotnet.a` gets included in the package alongside `libxamarin-dotnet.a`
3. At build time, make sure to link with the correct lib[tv]extension-dotnet.a library depending when we need to.
4. Add some tests.
Co-authored-by: Eric Sink <eric@Erics-MacBook-Pro.local>
Co-authored-by: Manuel de la Pena <mandel@microsoft.com>
Co-authored-by: Rolf Bjarne Kvinge <rolf@xamarin.com>
Rolf Bjarne Kvinge
Eric Sink