Drop-downs don't show all options when selecting one due to text filtering

[MaxGhenis]

For example, OG-USA has a few true/false drop-downs, which look like this initially:

But when selecting one, the drop-down no longer shows all the options, since it text-matches:

You can see other options by deleting the text in the text box, but I think a normal drop-down that shows all values would be more intuitive (maybe unless there are too many options to show, but I haven't seen that from any models yet).

[hdoupe]

@MaxGhenis We swapped to using the datalist HTML element from a dropdown like you are suggesting. The reason is that we need to support inputs like True,False,*,*,True in Tax-Brain so users can specify values for future years. The datalist gives the best of both worlds: you can select values from a dropdown while being able to type in your own value. However, it also has some disadvantages like what you've pointed out.

I'd love to replace this with something better. For example, the array input fields that we discussed in #311 could be extended to replace the wildcard syntax. However, the logic for getting this right is pretty complicated. This is my motivation for writing ParamTools.js which would expose richer ParamTools functionality on the client side and make it easier to support complicated inputs.