Golang x/tools/gopls/internal/analysis: add check for fmt.Sprintf("%s", x) -> x.String()

There are surprisingly many calls like

fmt.Sprintf("%s", x) // x implements Stringer

// or even,

fmt.Sprintf("%s", y.Name) // y.Name is a string

This could be edited to use x.String() in the first case and y.Name in the second.