DM-13065 adds a new low-level polynomials library to afw::math, incorporating but heavily modifying code from afw.math.ChebyshevBoundedField, meas.astrom.PolynomialTransform, and shapelet.

With a few small additions to the new polynomials library, we should be able to remove a lot of mostly-duplicate code in the shapelet package by delegating to the new new polynomials library. It may be cleanest if this involves some small API changes in shapelet, to allow some shapelet-specific objects to share interfaces with more general functionality.