ReplyToGetSetClearTest: test the setting of reply-to address in more depth
ReplyToGetSetClearTest: test the setting of reply-to address in more depth

This commit:
* Splits the primary tests previously contained in the `testAddressing()` method into two distinct test methods, each using a data provider to allow for adding additional test cases more easily.
* Enhances the tests by not only testing the return value of the `addReplyTo()` method, but also verifying that the `ReplyTo property has been set correctly and contains the expected information.

Includes adding `@covers` tags for these specific methods.

jimjag/PHPMailer,PHPMailer/PHPMailer,PHPMailer/PHPMailer,nawawi/PHPMailer,nawawi/PHPMailer,jimjag/PHPMailer