bug #64047 [Mime] Preserve inline part filename instead of overwriting it with the Content-ID (ousamabenyounes)

This PR was merged into the 6.4 branch.

Discussion
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[Mime] Preserve inline part filename instead of overwriting it with the Content-ID

| Q             | A
| ------------- | ---
| Branch?       | 6.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Issues        | Fix #62423
| License       | MIT

When an inline `DataPart` is matched against a `cid:` reference in an HTML body, `Email::prepareParts()` overwrites the part's name with the auto-generated `Content-ID` (e.g. `abcd...`@symfony``). That value then ends up as the `name=` parameter on both `Content-Type` and `Content-Disposition`, where it looks like a filename with an unsupported extension. Some mail providers reject the message with `5.7.1 Forbidden attachment type` (reproduced and acknowledged in #62423).

Before:

```
Content-ID: <divider-500x2@example.com>
Content-Type: image/jpeg; name="divider-500x2@example.com"
Content-Transfer-Encoding: base64
Content-Disposition: inline; name="divider-500x2@example.com";
 filename=divider-500x2.jpg
```

After:

```
Content-ID: <divider-500x2@example.com>
Content-Type: image/jpeg; name=divider-500x2.jpg
Content-Transfer-Encoding: base64
Content-Disposition: inline; name=divider-500x2.jpg;
 filename=divider-500x2.jpg
```

Only fall back to the `Content-ID` when the part has no name (preserves the previous behavior for inline parts created without a filename, e.g. raw `Email::embed()` callers that don't pass a name).

Commits
-------

97e613e9d69 [Mime] Preserve inline part filename instead of overwriting it with the Content-ID