go/types: embedded interface behavior now dependent on file name ordering [1.11 backport]

[gopherbot]

@ccbrown requested issue #28005 to be considered for backport to the next 1.11 minor release.

@gopherbot please consider this for backport to 1.11, it's a regression.

[gopherbot]

Change https://golang.org/cl/146660 mentions this issue: [release-branch.go1.11] go/types: use correct receiver types for embedded interface methods

[gopherbot]

Closed by merging 68ad1d6 to release-branch.go1.11.