[9.x ] Updated Mailable to prevent duplicated recipients

[WendellAdriel]

As discussed on #45042 these changes prevent the use of duplicated recipients in the to, from, cc, bcc and replyTo properties of the mailable.

[driesvints]

This looks okay to me. At least worth a try.

[WendellAdriel]

Thank you so much @driesvints!!!

[taylorotwell]

But now these tests no longer check that two "to" addresses can actually be added.

[WendellAdriel]

That’s true @taylorotwell, sorry!
I’ll update the tests and the PR ASAP

[AAllport]

It looks like this may have introduced a bug/breaking change...

If you have the following: Mail::to($recipient)->send(new FooMail($recipient))
You can no longer set the "name" of the recipient in the build method when calling ->to($reciepent->mail, $recipient->full_name)

It looks like the call to ->unique() is removing the instance of the address with the name.

Was this intended behaviour?
It feels like if you are calling ->to(), then the most recent addition should take priority.

Suggested fix in #45885