Hide some system schema fields from Results Table Editor

Currently, when configuring a results layout of a Page Provider in Designer (Layouts > [Page Provider ID] > results > table > switch to table editor), it is possible to drag and drop system schema fields like ecm:fulltext, ecm:mixinType and ecm:tag. This might cause problems when this configuration is deployed due to the special way these fields are handled by the platform (additional info in this comment by Ricardo).

There was an attempt to hide these when handling NXS-5257, but that part had to be reverted because the fields were made unusable not only there, but everywhere else, which ended up causing problems like NXS-5355.

The goal of this ticket is to investigate if these fields (and others from the system schema) can be used, and, if they cannot, to hide them from this editor (and others if the same conditions apply).