[netcore] More Array.Copy fixes (#13842)

[netcore] More Array.Copy fixes (#13842)

Remaining errors:
```
/Users/filipnavara/Documents/mono/mcs/class/corlib/System.Reflection/RuntimeMethodInfo.cs(391,0): at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
    System.Tests.ArrayTests.Copy_SZArray(sourceArray: [0, 1, 2, 3, null, ...], sourceIndex: 2, destinationArray: [204, 204, 204, 204, 204, ...], destinationIndex: 5, length: 3, expected: [204, 204, 204, 204, 204, ...]) [FAIL]
      System.InvalidCastException : Specified cast is not valid.
      Stack Trace:
        /Users/filipnavara/Documents/mono/mcs/class/System.Private.CoreLib/System/Array.cs(170,0): at System.Array.Copy(Array sourceArray, Int32 sourceIndex, Array destinationArray, Int32 destinationIndex, Int32 length, Boolean reliable)
        /Users/filipnavara/Documents/mono/mcs/class/System.Private.CoreLib/System/Array.cs(87,0): at System.Array.Copy(Array sourceArray, Int32 sourceIndex, Array destinationArray, Int32 destinationIndex, Int32 length)
        /Users/vsts/agent/2.149.2/work/1/s/src/System.Runtime/tests/System/ArrayTests.cs(1293,0): at System.Tests.ArrayTests.Copy(Array sourceArray, Int32 sourceIndex, Array destinationArray, Int32 destinationIndex, Int32 length, Array expected)
        /Users/vsts/agent/2.149.2/work/1/s/src/System.Runtime/tests/System/ArrayTests.cs(1243,0): at System.Tests.ArrayTests.Copy_SZArray(Array sourceArray, Int32 sourceIndex, Array destinationArray, Int32 destinationIndex, Int32 length, Array expected)
        /Users/filipnavara/Documents/mono/mcs/class/corlib/System.Reflection/RuntimeMethodInfo.cs(391,0): at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
    System.Tests.ArrayTests.SetValue_Casting_Invalid [FAIL]
      Assert.Throws() Failure
      Expected: typeof(System.InvalidCastException)
      Actual:   (No exception was thrown)
      Stack Trace:
        /Users/vsts/agent/2.149.2/work/1/s/src/System.Runtime/tests/System/ArrayTests.cs(3939,0): at System.Tests.ArrayTests.SetValue_Casting_Invalid()
        /Users/filipnavara/Documents/mono/mcs/class/corlib/System.Reflection/RuntimeMethodInfo.cs(391,0): at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
```

The last Copy_SZArray test case is `yield return new object[] { new object[] { 0, 1, 2, 3, null, 5, 6, 7, 8, 9 }, 2, new int?[] { 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 0xcc }, 5, 3, new int?[] { 0xcc, 0xcc, 0xcc, 0xcc, 0xcc, 2, 3, null, 0xcc, 0xcc } };`