Replace AMM calculations with simpler approach in estimate.js

[Chris-Hibbert]

What is the Problem Being Solved?

The current code to calculate prices for swaps on the AMM is spread across several files: calcFees, calcSwapPrices,getXY, core, invariants, and swap. Some have found it hard to follow. estimate.js was written to allow the UI to predict prices without requiring a round trip to the chain. It has a test that shows it behaves the same as the more complex solution. If estimate is easier to explain, it might be a good idea to use it for the AMM's own calculations.

Description of the Design

Replace the code. Add more thorough documentation in the code to show how it carries out the design in README.md.

Security Considerations

This shouldn't effect security.

Test Plan

Consider whether any test cases need to be added. Consider substituting estimate.js in the existing AMM tests.

[Chris-Hibbert]

It might also have much better performance. It's just math, and not a lot of sending messages or packing and unpacking parameters.

[Chris-Hibbert]

The AMM was removed in #7074