Add CEGQI BV linearization of additions and equalities over additions. (#1417)

Add CEGQI BV linearization of additions and equalities over additions. (#1417)

Adds support for linearizing additions w.r.t. to a variable.

For example,

a * x + b + c * d * -x = e + x

is rewritten to

x * (a - c * d - 1) = e - b.

This also adds an additional rewriting rule x * x = x --> x < 2.