ComboBox interaction bugs

[aswallace]

The FluentUI component has a lot of interaction bugs that need to be resolved:

• [ ] When text is entered in annotation combobox, clicking the 'x' goes to the next step instead of dismissing
• [ ] Weird text highlighting & case restriction in autocomplete
• [ ] Clicking inside & typing still doesn't open open menu by default
• [ ] Searched item does not always appear at the top of the search results
• [ ] Add styling in combobox callout for focus/active/selected
• [ ] Tab from callout sometimes advances the modal when it shouldn't
• [ ] Arrow down with menu open changes file selection in the background (yikes!)

Part of #96