Settle on a Signal `==` performance solution

Signals only emit values that are different from their current state. “different” means Signal does an == check. This is very convenient, and in general improves performance by eliminating redundant DOM calls, but can potentially be expensive in certain situations, e.g. when comparing large, almost identical Map-s.

Currently we have com.raquo.airstream.util.Ref to deal with this, but the wrapping is annoying to deal with. Perhaps I should provide some helpers to deal with wrapped values easier, but I’m not convinced that this is the best solution.

I will look more into this when I get the time to work on memoization in Laminar (https://github.com/raquo/Laminar/issues/38), I think there might be some common ground between these issues.

[raquo]

I implemented composeChanges pretty much as described here. So far I like using it. I’ll marinade on this for a while, and will likely follow the general idea from my last comment.

[fdietze]

Comparing with == might be expensive, but has no surprises. so it should be the default.

I can think of several options for giving users more control over performance:

• write own equals method
• disable comparison for specific types
• disable comparison for specific nodes in the dataflow-graph