The names given to methods of types created during type substitution
were possible incorrect when the type parameters themselves were nested
types.
Fixes#50485
Change-Id: I7e0043ed22c26406a5f9d8d51d9e928770a678f6
Reviewed-on: https://go-review.googlesource.com/c/go/+/377494
Reviewed-by: Keith Randall <khr@golang.org>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
