MessagePathInput closes automatically when you type a full topic name

[jtbandes]

If you are typing in the field, and you happen to type out a complete topic name, it closes the autocomplete. Ideally the autocomplete would stay open so that if you were looking for a subfield, you can still see and select it from the list.

Originally posted by @jtbandes in https://github.com/foxglove/studio/issues/2698#issuecomment-1016793466