[dagit] Fix Asset search selection
Repair asset search typeahead selection behavior.
- Fix using keyboard to choose items when a querystring is in use
- Allow cycling through results with keys
- Fix resetting highlight and dropdown visibility when text changes
View Asset search, verify that I can choose the correct items with mouse and keyboard, whether or not a querystring is in use.
Type a character, press escape to hide dropdown. Type something else, verify that it reappears.
Reviewers: bengotow, sandyryza, sashank
Reviewed By: bengotow
Differential Revision: https://dagster.phacility.com/D6606