DiagnosticForError computes a diagnostic suggesting to implement an interface to fix the type checking error defined by (start, end, msg).

GetStubInfo determines whether the "missing method error" can be used to deduced what the concrete and interface types are.

MatchesMessage reports whether msg matches the error message sought after by the stubmethods fix.

recognized by gopls ApplyFix.

StubInfo represents a concrete type that wants to stub out an interface type.