New Issue: Non-nilable types in resized arrays, associative arrays, and sparse arrays

17720, "ben-albrecht", "Non-nilable types in resized arrays, associative arrays, and sparse arrays", "2021-05-13T16:18:04Z"

This is a continuation of #15394 to track the last mile of the type-collection
matrix marathon. Since the creation of #15394, it has been determined that
resized arrays, assoc arrays, and possibly sparse arrays should support
non-nilable types.

✅ = currently works
❌ = currently does not work
🔹 = not expected to work
❔ = still up for debate on whether it is expected to work (❌) or not (🔹)