assertSeeInOrderText and assertSeeInOrderHtml for Mailable

[JHWelch]

While testing a Mailable's content, I noticed that it has assertSeeInText and assertSeeInHtml, but does not have an equivalent of \Illuminate\Testing\TestResponse's assertSeeInOrder.

This would be useful for testing the structure of an email.

This seems like it would not be too hard to implement. I could use the same Illuminate\Testing\Constraints\SeeInOrder class that the TestResponse uses.

Is this something people would want? I am willing to do the work.

And if it is something people would want, would it make sense to have assertSeeInOrderText and assertSeeInOrderHtml as those mirror the existing assertions. Also open to better names, those feel a little clunky.

Example of how this would be useful.

I have an email notification with chores past due and dude today that are listed in order of due date, under separate headings.

Markdown looks something like

## Past Due
- Past due chore 1
- Past due chore 2
## Due Today
- Due today chore 1
- Due today chore 2

And I want to test the structure with

$daily_digest = new DailyDigest($user);

$daily_digest->assertSeeInOrderText([
    'Past Due',
    'Past due chore 1',
    'Past due chore 2',
    'Due Today',
    'Due today chore 1',
    'Due today chore 2',
]);

[JHWelch]

Added this in #40460