Problem:

Currently, attempting to create a new Item in commons via the Special:NewItem page results in a database error message (see error report at T333574). To mitigate this issue, we should catch the error before it reaches the database by checking to see if the Item entity type is supported on the current site. If it is not supported on the current site, we will throw a more helpful error message.

Acceptance Criteria:

• Attempting to create a new item in Commons via the Special:NewItem page results in a more helpful error message.
• The error message clearly indicates that the Item entity type is not supported on the current site.