cmd/compile: fix method expression lookup during import

cmd/compile: fix method expression lookup during import

CL 309831 fixed importing of method expressions, by re-using the same
code already have for ODOTMETH. But that code does not work with
embedded field.

To fix this, we need to calculate all methods of the receiver base type
of method expression, before looking up the selection.

Fixes #48088

Change-Id: Ia244d36a3ed0f989735eb57becdfa70a81912f57
Reviewed-on: https://go-review.googlesource.com/c/go/+/346489
Trust: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>