Runtime styling types with IDs should conform to Identifiable

[1ec5]

The Annotation, AnnotationManager, Layer, and SourceInfo protocols have the property id, which would satisfy the requirements of the Swift standard library’s Identifiable protocol. These protocols might as well explicitly conform to Identifiable as a formality.

Note that this feature request applies only to protocols that already define an id property. The Identifiable protocol also provides a default implementation for AnyObject that most likely returns the object’s memory address, something that probably would not be expected.

/ref mapbox/turf-swift#165
/cc @mapbox/maps-ios