Clarify the type of Constrainable Properties

[jan-ivar]

This spec still conflates constraints and constrainable properties in places (the former are applied to the latter).

One instance is its description of types of constrainable properties (skip deviceId and groupId for now due to #941, and skip integer ones due to #944):

This is wrong and misleading.

The type of the constrainable property, the property being constrained on, is a simple type, not a Constrain* dictionary.

E.g. the type of the constrainable property frameRate is double, not ConstrainDouble.

This didn't used to matter, but with #766 it is causing confusion, e.g. in #933.

[jan-ivar]

I'm marking this as editorial as these mistakes seem attributable to editing of the spec over time to move away from "constraints" as the primary concept, to "constrainable properties" being the primary concept, and at some point this was probably a list of constraints, not constrainable properties (points to #258).