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.

This library duplicates a lot of the functionality in afw/math/FunctionLibrary.h, but avoids virtual functions and hence can be used in more performance critical areas. We should try to have the polynomials in FunctionLibrary.h delegate to the new polynomial library.