go/types: postpone interface method type comparison to the end

Introduce a new list of final actions that is executed at the
end of type checking and use it to collect method type comparisons
and also map key checks.

Fixes #33656.

Change-Id: Ia77a35a45a9d7eaa7fc3e9e19f41f32dcd6ef9d9
Reviewed-on: https://go-review.googlesource.com/c/go/+/191418


Reviewed-by: Alan Donovan <adonovan@google.com>