preserve placement of comment directives relative to variable declarations

[buyology]

This package:

package p

import "embed"

//go:embed *
var fs embed.FS
var s string

gets gofumpted to

package p

import "embed"

//go:embed *
var (
	fs embed.FS
	s  string
)

which no longer compiles (./embed.go:5:3: misplaced go:embed directive) since the comment directive is moved above the variable group.

[mvdan]

Thanks, definitely sounds like a bug.