go/types: validity of program depends on method declaration order #23203
Description
https://play.golang.org/p/WCktUidLyc_ is accepted while the equivalent program https://play.golang.org/p/Z-B9rBhYILd fails with an error. The only difference is the order of the method declarations.
Esoteric case, but may not be too hard to get right. Marking for 1.11 in case we get to it.
See also #23202.