Layouts: Visibility conditions available when one of two required contexts are missing

Description of the bug

When creating a User compare context (to compare my user account to the user account for the profile page I am viewing, for example) I noticed that even though contexts were marked as required, the visibility condition is still visible in the drop-down menu.

This new visibility condition has two required user contexts, so should not be available on any path without a user context (the second user context is global $user and is always available). Yet it appears in the select list for the home page layout.

Steps To Reproduce

To reproduce the behavior: 1. Apply the patch from https://github.com/backdrop/backdrop-issues/issues/4029 2. Manage blocks on the home page layout 3. Attempt to add a visibility condition

Actual behavior

4. Confirm that User: compare appears in the list

Expected behavior

Since User: compare appears in the list has required contexts that are not present, User: compare should NOT appear in the list of available visibility conditions