The zoom level 19 tiles are now available, the UI must be adapted to allow zooming to level 19.
Verification list:
(checked items are complete with the patch)
- Mapframe embedded view (includes the pre-set zoom parameter)
- Mapframe expanded view
- Maplink zoom parameter
Note, that maplink zoom parameter works in the sense that it produces the correct link (with data-zoom=19 etc) but it "fails" now becaues maps.wikimedia.org display zoom 18 for the moment.
See T186780: Enable zoom 19 in tilerator / kartotherian UIs for the kartotherian UI piece.