This patch adds a linear polynomial base class, called LinearPolyBase, which

serves as a base class for StackOffset. It tries to represent a linear

polynomial like:

c0 * scale0 + c1 * scale1 + ... + cK * scaleK

where the scale is implicit, meaning that only the coefficients are

encoded.

This patch also adds a univariate linear polynomial, which serves as

a base class for ElementCount and TypeSize. This tries to represent a

linear polynomial where only one dimension can be set at any one time,

i.e. a TypeSize is either fixed-sized, or scalable-sized, but cannot be

a combination of the two.

class LinearPolyBase ^ | +---- class StackOffset (dimensions = 2 (fixed/scalable), type = int64_t) class UnivariateLinearPolyBase | | +---- class LinearPolySize (dimensions = 2 (fixed/scalable)) ^ | +-------- class ElementCount (type = unsigned) | | +-------- class TypeSize (type = uint64_t)