As pointed out in #47916, the IsConstraint method becomes ambiguously
named if ever we allow interfaces with structural restrictions outside
of constraint position.
Add instead an IsMethodSet method, which has the opposite sense and
avoids this ambiguity. In a subsequent CL the IsConstraint method will
be removed, once x/tools has been updated to use the IsMethodSet API.
Updates #47916
Change-Id: I82ad16b111464b0cd2f354b8ecdd4b3f14796cd9
Reviewed-on: https://go-review.googlesource.com/c/go/+/352616
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Robert Griesemer <gri@golang.org>