remove newlines right after an assignment operator

[mvdan]

The following isn't modified by gofmt nor gofumpt:

package main

func main() {
	foo :=
		"bar"
}

We should probably not allow such a newline. I would have guessed that it was valid Go, but that gofmt would not allow it.

I'm trying to think of a scenario where it would make sense, but I can't. There isn't any consistency with a closing token on a separate line here. The only possibly reasonable use case I can think of is:

foo :=
    `
        multi-line
        content
    `

Which someone could think is a tiny bit nicer than:

foo := `
        multi-line
        content
    `

Still, I don't think it's worth the weird syntax and extra newline/verbosity.