Schema dropdown on node creation should show other schemas

It is confusing when trying to create a new node but the intended schema does not show up because the schema is not assigned to the project. Maybe it would be better to show the schema greyed out and add a tooltip that hints the user to assign the schema.

Start by locating the node-creation form and its schema dropdown, then inspect how schemas unavailable to the current project are filtered. Done means an unassigned intended schema remains visible but greyed out and provides a tooltip explaining that it must be assigned to the project.

Written by the indexing model from the issue text.