Ensure that we correctly type the stack temps for regular closures,
method function closures, and slice literals.

Then we don't need to override the dummy types later.
Furthermore, this allows order to reuse temporaries of these types.

OARRAYLIT doesn't need a temporary as far as I can tell, so I
removed that case from order.

Change-Id: Ic58520fa50c90639393ff78f33d3c831d5c4acb9
Reviewed-on: https://go-review.googlesource.com/c/140306Reviewed-by: Cherry Zhang <cherryyz@google.com>