rewriting the autocompleting text field

[yshavit]

This rewrite puts all of the options into a single text view, instead of having each one as a separate NSView. The result is at least a couple orders of magnitude difference; I'll do some benchmarking in a bit.

The old implementation made the ⌘F find feature borderline unusable because of how slow it was. Now it won't quite be snappy, but it'll at least be usable.

[yshavit]

Some numbers:

	Load the options	Open the popup	Type a char	Delete a char
Before	4.3 seconds	~7 seconds¹	~3 seconds	~9 seconds³
After	0.15 seconds	milliseconds²	milliseconds²	milliseconds²

_{1. I couldn't figure out how to time the UI elements; even when I enqueue a work item using DispatchQueue.async with a QoS of userInteractive, the timer completes well before the actual change appears on the UI. So, I'm manually starting a stopwatch to time it, and it's thus subject to my thumb reaction time. Any column marked with "~" is approximate because of this.}

_{2. Using the stopwatch method described above, these were basically all "noticeable, but too fast for me to time."}

_{3. Deleting a char takes longer than typing one, because it means that by the end of the action, there are more options visisble.}