eliminate need for "interactive" property on layers

[jfirebaugh]

All layers should support featuresAt automatically. Behind the scenes the necessary datastructures should be built lazily, or however makes sense for performance.

Having a user-visible interactive layer property leaks implementation details to the API, is a big trap for users, and leads to convoluted examples like this.

[ansis]

I did some profiling and memory usage is fine when we remove interactive and make it enabled for all layers. and it could probably be optimized further.

The main task updating the style spec: mapbox/mapbox-gl-style-spec#418

Should we wait until the spec is changed and released or can we start ignoring it immediately?

[lucaswoj]

I don't think we need to wait until the spec is changed.

That said, we do need to think carefully about this because it is a breaking change. Users who do not pass a layer parameter might expect only features from interactive: true layers to be returned.

[tmcw]

🎉 🎉 🎉 this is excellent news thx @ansis