Don't warn about parameters in grouped types unless all apply

[mvdan]

For example:

func Transfer(from, to SomeStruct) {
    b := make([]byte, 10)
    from.Read(b)
    to.SomeOtherMethod(b)
}

from could be an io.Reader, but to a human this doesn't make much sense.

[mvdan]

To clarify, if both from and to could be replaced by a better type, then we should produce the warning.