Eliminate the syntactic distinction between "paint" and "layout" properties

[lucaswoj]

The differences between "paint", "layout", and "top-level" properties are becoming increasingly nuanced. Without a firm knowledge of our implementation, it can be hard to reason about the behaviour of paint properties vs layout properties, especially in the context of data-driven styling. It is worth considering eliminating the syntactic distinction between "paint" and "layout" properties (as Studio does), instead providing documentation about the behaviour of each property.

[nickidlugash]

This sounds good generally, but just want to flag that it may make the definition of a ref sound more convoluted.

[lucaswoj]

@nickidlugash We're getting rid of refs too 😄 As of now, ref is a no-op in GL JS.

[lucaswoj]

This issue was moved to mapbox/mapbox-gl-js#4160