applets/notifications: allow screen reader to read notification
This enables Orca to read notification summary and body.
| Type | Accessible.name | Accessible.description |
|---|---|---|
| Popup | {Summary} |
{Body} from {Application Name} |
See also https://codereview.qt-project.org/c/qt/qtdeclarative/+/441777
Requires qt/qt/qtdeclarative!30 (merged)