Class-specific paint properties in runtime styling API

[1ec5]

Per #5727 (comment), paint attributes are exposed, unparameterized, at the top level of each style layer class. For non-default, style class–specific paint properties, we should add an additional pair of getters and setters for each attribute. For example, the circleBlur property should be accompanied by -circleBlurForStyleClass: and -setCircleBlur:forStyleClass:.

/cc @frederoni @jfirebaugh

[jfirebaugh]

What if we didn't expose class-specific paint properties in the SDK? Android doesn't, and I'm 95% sure that we'll be removing them from the style specification in a future revision.

[1ec5]

Style classes have been in limbo for well over a year. The point of this ticket is that, if we intend to keep style classes around, then we should make them usable. If they're deprecated, though, I agree that we should focus our efforts elsewhere.

[jfirebaugh]

Let's focus our efforts elsewhere.