Complete generic parameter support for windows-rdl

[Kenny Kerr (kennykerr)]

Building on #3861, this completes support for not only generic types (#3902) but also generic parameters which require special handling as per the spec. This update allows the following:

#[winrt]
mod Test {
    delegate fn Handler<Arg, Result>(arg: Arg) -> Result;

    interface IMap<K, V> {
        fn Lookup(&self, key: K) -> V;
        fn Handler(&self, handler: Handler<K, V>);
        fn Generic(&self, map: IMap<K, V>);
        fn Special(&self, map: IMap<i32, u64>);
    }
}

Notice how thew handler and map parameters can both inherit the generics of the enclosing type or be specialized directly. And here is the result IL:

.class interface public auto ansi abstract windowsruntime Test.IMap`2<K, V>
{
	.method public hidebysig newslot abstract virtual 
		instance !V Lookup (
			[in] !K key
		) cil managed 
	{
	}

	.method public hidebysig newslot abstract virtual 
		instance void Handler (
			[in] class [Test]Test.Handler`2<!K, !V> 'handler'
		) cil managed 
	{
	}

	.method public hidebysig newslot abstract virtual 
		instance void Generic (
			[in] class [Test]Test.IMap`2<!K, !V> map
		) cil managed 
	{
	}

	.method public hidebysig newslot abstract virtual 
		instance void Special (
			[in] class [Test]Test.IMap`2<int32, uint64> map
		) cil managed 
	{
	}
}

Next up I need to work on required interfaces (that can also be generic).