R=go1.11

The existing code associated methods with receiver base type
names before knowing if a type name denoted a locally defined
type. Sometimes, methods would be incorrectly associated with
alias type names and consequently were lost down the road.

This change first collects all methods with non-blank names
and in a follow-up pass resolves receiver base type names to
valid non-alias type names with which the methods are then
associated.

Fixes #23042.

Change-Id: I7699e577b70aadef6a2997e882beb0644da89fa3
Reviewed-on: https://go-review.googlesource.com/83996Reviewed-by: Alan Donovan <adonovan@google.com>