[Bridge] [Swiftmailer] adds deprecation notice on MessageDataCollector class.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | yes
| Tests pass?   | yes
| Fixed tickets | ~
| License       | MIT
| Doc PR        | ~
I would move the trigger at the top of the class like done in other deprecated classes. Also, can you put the message on one line only? You can replace the class name with `__CLASS__` to make it a bit shorter and instead of giving the URL to pakcagist, just mention the package name.