…7755)

* fix: prevent trying to remove already removed

Sometimes, the call to `removeCellCustomEditor` can be done to a widget
already removed from its parent, which causes a client-side error.

This change try to address that with some refactor on the custom editors
internal map.

The refactor aims to replace the keys that currently refer to the cell
address with the editor ID itself. That way, in case the same editor is
shared by more than one cell, the same `Slot` will be used. With the
current logic, more than one `Slot` element would be created for the
same editor, which could cause issues like, the editor not being shown
because it was moved to the other `Slot` parent.