go/types, types2: nonsensical error message and position when type argument does not match constraint

[findleyr]

When a function is instantiated with type arguments that don't satisfy its type parameter constraints, the error message go/types produces references the type parameter, rather than the type argument, and is also located on the parameter.

Example (this error check test currently passes in go/types):

package p

func app[S  /* ERROR "type S = S does not match" */ interface{ type []T }, T any](s S, e T) S {
        return append(s, e)
}
                                                                                                                                                    
func _() {
        _ = app[int]
}

In this case, the actual error is that app is instantiated with int rather than []int.

Confirmed that this also affects types2.

CC @griesemer

[gopherbot]

Change https://golang.org/cl/317471 mentions this issue: go/types: add a test case for issue 45985

[gopherbot]

Change https://golang.org/cl/317732 mentions this issue: cmd/compile/internal/types2: add test case for issue 45985

[gopherbot]

Change https://golang.org/cl/362634 mentions this issue: cmd/compile: fix type error reported on the wrong line