Optimize static switches

[RunDevelopment]

Fixes #2262.

This adds a backend compiler optimization that statically executes (kinda) the Switch node if the selected input is statically known (it currently always is). Static execution is a strong word. In actuality, it just removes the edges from inputs that aren't selected. However, the effect is the same: only the selected input will be executed.

Of course, this new optimization works together with the already present removed_dead_nodes optimization.

Other changes:

• To implement this optimization, I also had to make some (long overdue) changes to the Chain. It now contains node input values instead of just edges. Since optimization may add, change, and remove nodes, they also need to be able to influence input values.
• Optimization now use mutation signal instead of returning a bool to say that they changed the chain. This just makes optimizations a little easier to implement.
• Use data classes in a few places.
• The executor now derives the input map it used from the given chain.