1. Look for declarations in the current submission (including aliases).
 2. Look for declarations in preceding submissions (including aliases), in
 order.
 3. Look for members in the host object (if any).
 4. Look for declarations in the global namespace.
 5. Look in usings (except aliases) in the current submission and all
 preceding submissions (all at once, not looping).
 6. Look in the global imports of the current submission and all preceding
 submissions (all at once, not looping).

Note that 5, 6, and aliases from 1 are skipped if we are binding the
target of a using in the current submission.

Fixes #5450
Fixes #4811