Update proxies so you can pass typed arrays to Vertex/Index buffers' SetData/GetData.
Checkpoint: Do type substitution when applying packed struct array attributes so that you don't get IPackedStructArray<!!0> and nonsense like that.
Do type substitution in the packed array support more narrowly because ILSpy type substitution is still totally busted
Fix compiler-generated property backing stores from proxies being introduced erroneously into proxied types.
Expand struct allocation hoisting to work against method references that can't be resolved. This allows it to operate on PackedArray set_Item calls.
Use runtime dispatch for PackedArray's Length property to make fetching it cheaper.
Only ever create a single temporary local variable per function for a given type when doing allocation hoisting (separate temporaries aren't necessary)
Fix a bug in the Stream.Read baseline implementation and add type hints