Can't create Leaflet Attachment view display on Search API Index

@vierlex sorry ... I commented on this, but didn't save and send it probably.

When I took this module in its D8 alpha state the following Leaflet Views plugins where there as drafted, and totally unusable:

- modules/leaflet_views/src/Plugin/views/display/LeafletAttachment.php (@ViewsDisplay);
- modules/leaflet_views/src/Plugin/views/row/LeafletMarker.php (@ViewsRow);
- modules/leaflet_views/src/Plugin/views/style/Leaflet.php (@ViewsStyle);

and they still are now.
I couldn't fix them, both because I din't have time and also because I couldn't figure out their original (requested) function, and still cannot.

In the last commit (and Leaflet 8.x-1.5 version) I made them hidden from the UI, with this annotation index: no_ui = TRUE,
as really they are buggy and un-usable at the moment, and would need deep review, refactoring, fix.
But I am not going to spend my time on that at the moment ...
That's why this won't fix.

You can start from their actual state and fix them, deploying a well tested, php/drupal 8 coding compliant and not regressive patch, if you can.
And then reopen this issue ...
Or, probably more opportunely, even open a new Feature Request on them.