go/types, types2: optimize Named type method lookup
Because methods associated with named types are in the
same package as the type, when looking up a method we
don't need to check the package repeatedly.
Rename the global lookupMethod function to methodIndex,
to match the corresponding fieldIndex function (cleanup).
Implement Named.methodIndex, optimized for method lookup
on named types (optimization).
Adjust call sites.
Change-Id: Ifa05306126773262b1af3ce73365b5742b470eb6
Reviewed-on: https://go-review.googlesource.com/c/go/+/562297
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Robert Griesemer <gri@google.com> Reviewed-by: Robert Findley <rfindley@google.com> Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>