Color.js objects cannot be wrapped in a Proxy (and thus, cannot be used with Vue or other Proxy-based libraries)

[LeaVerou]

Due to using private properties, every time a Color instance is wrapped in a Proxy, errors are just around the corner.

For context, see:

• https://twitter.com/LeaVerou/status/1650562320702099457
• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy#no_private_property_forwarding
• Error when property value is an instance of a class using private class fields vuejs/core#8149
• Private members break proxies tc39/proposal-class-fields#106

We only use a single private property: #space, and it's primarily to ensure color space is immutable. We can just use Object.defineProperty() instead and be done with it.

Edit: There is actually a bunch more privates in space.js but nothing too hard to refactor out.

[LeaVerou]

It is actually worse than I thought: this even affects plain color objects, as they still use ColorSpace objects.

It is unclear if there is a way to definitively check color space equality without using object equality. In #306 I fall back to string comparison of ids, but that's …not great.