cmd/compile: improve "have X want Y" error with additional file and line information

[raspi]

What version of Go are you using (go version)?

go1.15.5 linux/amd64

Does this issue reproduce with the latest release?

Yes

What did you do?

package main

type S interface {
	DoSomething() (int, error)
}

type myS struct{}

func (s myS) DoSomething() (string, error) {
	return ``, nil
}

func main() {
	var _ S = &myS{}
}

What did you expect to see?

Show also line information (foo.go:123:57) for have line. The implementation might be in completely different file. In modern IDEs you simply can click the file information line to navigate to referenced file and line quickly.

want could also have line information to referenced interface definition line?

./prog.go:14:6: cannot use &myS literal (type *myS) as type S in assignment:
	*myS does not implement S (wrong type for DoSomething method)
		have DoSomething() (string, error) at ./prog.go:9:28
		want DoSomething() (int, error)

What did you see instead?

./prog.go:14:6: cannot use &myS literal (type *myS) as type S in assignment:
	*myS does not implement S (wrong type for DoSomething method)
		have DoSomething() (string, error)
		want DoSomething() (int, error)

[networkimprov]

cc @mdempsky @griesemer

Seems overlooked by triage?