Add "Clear Field" button for text inputs

When working with Symbols, we like to use logic to allow a field to be overridden if populated but provide a secondary fallback if the value is nullish. Unfortunately, if you just empty the text in an input right now, it leaves it as an empty string which breaks our nullish coalescing. To fix it, we have to go into the JSON View and remove the field.

It'd be nice to have a Clear button that would just do that automatically. ;)