go/types, types2: tweak missingMethodReason logic to improve message

This makes the error case pointed out in the issue like the current
message in Go 1.17 or -G=0 mode. The priority is to point out the
similar but wrong method name, rather than a difference in type.

Made changes to both cmd/compile/internal/types2 and go/types.
Added in a missing tab in an error message in go/types.

At the same time, removed the extra "at info" on the have lines (and
pointer receiver lines) of error messages, as requested in #50907.

Fixes #50816
Fixes #50907

Change-Id: I04f8151955bdb6192246cbcb59adc1c4b8a2c4e5
Reviewed-on: https://go-review.googlesource.com/c/go/+/381774


Reviewed-by: Robert Griesemer <gri@golang.org>
Trust: Dan Scales <danscales@google.com>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>