Simplify the implementation of interface conversions in the compiler.
Don't pass fields that aren't needed (the data word, usually) to the runtime.
For generics, we need to put a dynamic type in an interface. The new
dataWord function is exactly what we need (the type word will come
from a dictionary).
Change-Id: Iade5de5c174854b65ad248f35c7893c603f7be3d
Reviewed-on: https://go-review.googlesource.com/c/go/+/340029
Trust: Keith Randall <khr@golang.org>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Dan Scales <danscales@google.com>