Mono used to return `true` for these three cases (see System.Reflection.Tests.TypeTests.IsAssignableFrom tests):
```csharp
using System.Reflection;
using Xunit;

namespace ConsoleApp
{
    public static class Program
    {
        static void Main(string[] args)
        {
            Assert.False(typeof(TI_Interface1[]).GetTypeInfo().IsAssignableFrom(
                         typeof(TI_StructWithInterface[]).GetTypeInfo()));

            Assert.False(typeof(int?[]).GetTypeInfo().IsAssignableFrom(
                         typeof(int[]).GetTypeInfo()));

            Assert.False(typeof(int[]).GetTypeInfo().IsAssignableFrom(
                         typeof(int?[]).GetTypeInfo()));
            
        }
    }
    
    public interface TI_Interface1 { }
    public struct TI_StructWithInterface : TI_Interface1 { }
}
```
Fixes #10848
Fixes #15080

Unrelated  System.Reflection.MetadataLoadContext.Tests tests that don't fail anymore:
Close #15351
Close #15348
Close #15347
Close #15346
Close #15345
Close #15343
Close #15342
Close #15341
Close #15338
Close #15337
Close #15336