Support ref locals/refturn

[adrianoc]

It looks like we already have a lot of support; i.e, code like

using System;
class Foo
{
	int field;
	ref int M(ref int i) => ref field;

	ref int Local() 
	{
		ref int l = ref field;
		return ref l;
	}

	ref int Property
	{
		get
		{
			ref int l = ref field;
			return ref l;
		}
	}
}

Looks to be generating correct code.

Tasks

• Add tests (if we don't have any) and fix any failures

Cover

• Ref return
• Local refs
• Methods returning refs
• Property returning refs

MSDN Docs

https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/ref-returns