* Add support for specifying custom entitlements with an MSBuild item group.
* Use this new support to automatically add the 'com.apple.security.cs.allow-jit'
entitlement to .NET desktop apps when building for release, since all apps that
go through notarization will need it in order to be able to use the JIT.
It's possible to override the default behavior by adding something like this to the project file:
<ItemGroup>
<CustomEntitlements Include="com.apple.security.cs.allow-jit" Type="Remove" />
</ItemGroup>
Fixes https://github.com/xamarin/xamarin-macios/issues/15745.