feat: imports grouping

[MilkeeyCat]

This pr changes formatter to keep a new line between imports. For example, if you had such code:

package main

import (
	"fmt"
	"strings"

	"strconv"
)

var _, _ = fmt.Print("")
var _ = strings.Index("", "")
var _ = strconv.Quote("")

It would remove the empty line, but now it doesn't.

closes #939

[a-h]

Looks good, could you add a test please?

Should be fairly easy to add something to the txtar files in testdata, as per https://github.com/a-h/templ/blob/main/cmd/templ/imports/testdata/namedimportsadd.txtar

[MilkeeyCat]

groups.txtar

-- fmt.templ --
package test

import (
	"strings"
	"fmt"

	"strconv"
)

var _, _ = fmt.Print(strings.Contains(strconv.Quote("Hello"), ""))
-- fmt.templ --
package test

import (
	"fmt"
	"strings"

	"strconv"
)

var _, _ = fmt.Print(strings.Contains(strconv.Quote("Hello"), ""))

Something like this?

[a-h]

Yes, but if there's any other behaviour to consider, like what happens if there's two line breaks, something to cover those scenarios would also be helpful.

Thanks!

[a-h]

Thanks for that, much appreciated!