[base] CORDIC improvements. The scaling between the hypotenuse and its CORDIC approximation is based on regression analysis. The smaller padding for `theta' is justifed by its maximum error of less than 6. * src/base/fttrigon.c (ft_trig_downscale): Borrow code from ./ftcalc.c (ft_multo64), change linear intercept. (ft_trig_pseudo_polarize): Decrease `theta' padding.