-tintColorDidChange will not be called if the color is changed before a layer-backed node loads

[nguyenhuy]

After #1620, developers can expect that:

• Change tint color after a view-backed node loaded: tintColorDidChange will be called immediately.
• Change tint color before a view-backed node loads: tintColorDidChange will be called when the node loads. This is because when we load the node's view and apply pending state to it, the view will call tintColorDidChange on itself which will call the node's counterpart (see -[_ASDisplayView tintColorDidChange]).
• Change tint color after a layer-backed node loaded: tintColorDidChange will be called immediately.
• Change tint color before a layer-backed node loads: tintColorDidChange will not be called, even when the node loads.

A more developer-friendly API should make sure the same behavior applies regardless of whether the node is view-backed or layer-backed.

We should also see if we can support the same behaviors for wrapper nodes (nodes that wrap around normal UIView objects via -initWithViewBlock:). Our -[_ASDisplayView tintColorDidChange] hook doesn't work in this case, so we may have to swizzle.