[Bridge] [Swiftmailer] removes Swiftmailer bridge namespace.
[Bridge] [Swiftmailer] adds deprecation notice on MessageDataCollector class.
minor #13056 [2.7] [Bridge] [Swiftmailer] adds deprecation notice on MessageDataCollector class. (hhamon)

This PR was merged into the 2.7 branch.

Discussion
----------

[2.7] [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        | ~

Commits
-------

c003bb1 [Bridge] [Swiftmailer] adds deprecation notice on MessageDataCollector class.
Merge branch '2.7'

* 2.7:
  [Bridge] [Swiftmailer] adds deprecation notice on MessageDataCollector class.
feature #13046 [3.0] [Bridge] [Swiftmailer] removed Swiftmailer bridge namespace. (hhamon)

This PR was merged into the 3.0-dev branch.

Discussion
----------

[3.0] [Bridge] [Swiftmailer] removed Swiftmailer bridge namespace.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | ~
| License       | MIT
| Doc PR        | ~

Commits
-------

c70a616 [Bridge] [Swiftmailer] removes Swiftmailer bridge namespace.