Master ticket tracking expression API completeness

[anandthakker]

This ticket is intended to define what set of operators would constitute a "complete" expression API and track its implementation.

• Math https://github.com/mapbox/mapbox-gl-js/issues/5853
  • [ ] All the Math.* functions from Javascript
  • [ ] All the relevant functions from NSExpression
  • [x] is-nan https://github.com/mapbox/mapbox-gl-js/issues/5494
• Geo
  • [ ] Haversine distance https://github.com/mapbox/mapbox-gl-js/issues/6062
• Color
  • [ ] All the color-modifying functions from CSS4 https://github.com/mapbox/mapbox-gl-js/issues/5676
• Arrays
  • [ ] Construction https://github.com/mapbox/mapbox-gl-js/issues/6155
  • [x] Search https://github.com/mapbox/mapbox-gl-js/issues/4698
  • [ ] Slicing
  • [ ] Join
• Strings
  • [x] Search https://github.com/mapbox/mapbox-gl-js/issues/4113 (but see also Regular Expressions)
  • [ ] Replace https://github.com/mapbox/mapbox-gl-js/issues/4100 (but see also Regular Expressions)
  • [ ] Slicing
• [ ] ~Regular Expressions https://github.com/mapbox/mapbox-gl-js/pull/6228~
• Locale and language
  • [x] Test for script support https://github.com/mapbox/mapbox-gl-js/issues/5807
  • [x] Case and diacritic folding https://github.com/mapbox/mapbox-gl-js/issues/4136
• Date and time
• Reflection into style state
  • [x] Style image availability https://github.com/mapbox/mapbox-gl-js/issues/5261