[9.x] Migrate mail components (#44527)

* allow framework mail component to be used as anonymous components

* refactor button component

* migrate header

* refactor message

* reinstate url

* BC fix for old component syntax

* migrate markdown stub

* fix test

* refactor text layout

* migrate notification

* fix attributes

Author: timacdonald

resources/views/email.blade.php

@@ -1,4 +1,4 @@
-@component('mail::message')
+<x-mail::message>
 {{-- Greeting --}}
 @if (! empty($greeting))
 # {{ $greeting }}
@@ -24,9 +24,9 @@
         default => 'primary',
     };
 ?>
-@component('mail::button', ['url' => $actionUrl, 'color' => $color])
+<x-mail::button :url="$actionUrl" :color="$color">
 {{ $actionText }}
-@endcomponent
+</x-mail::button>
 @endisset
 
 {{-- Outro Lines --}}
@@ -45,14 +45,14 @@
 
 {{-- Subcopy --}}
 @isset($actionText)
-@slot('subcopy')
+<x-slot:subcopy>
 @lang(
     "If you're having trouble clicking the \":actionText\" button, copy and paste the URL below\n".
     'into your web browser:',
     [
         'actionText' => $actionText,
     ]
 ) <span class="break-all">[{{ $displayableActionUrl }}]({{ $actionUrl }})</span>
-@endslot
+</x-slot:subcopy>
 @endisset
-@endcomponent
+</x-mail::message>