R1:d2bca2f32da0

Fix call to non-existing getTransactionCommentForSave() in PhabricatorInlineComment

Summary:
rPb48a22bf50a32895566e9aa66c1d7aff87a492b8 moved the call `$this->getTransactionCommentForSave()->save()` from within `PhabricatorAuditInlineComment` to the new (parent) class `PhabricatorInlineComment.php`, however the later does not define this function.

As the two child classes which extend `PhabricatorInlineComment` both implement `getTransactionCommentForSave()`, declare an abstract function in their parent…