Adding an inline form to discussion list page leads to noticeable performance problems

This is a followup / regression/ related of MDL-65069.

Performance tests detected that, with that issue integrated, a good number of things went noticeably up. This is the summary:

While some of them can be understandable (files included, slight memory grow...) because all the forms machinery is being included in a page that was forms-free before... there is a BIG increase in database queries that we have failed to find any justification.

Note that there is another issue, MDL-65429, pre-existing, that has been created, but that does not explains any of the differences. Here there is a list of the most used queries with and without MDL-65069.

We should aim to reduce them, particularly in that case (view forum / list discussions) and, in general, if possible... everywhere. Adding an empty form shouldn't lead to that.

Ciao