Function matrix_mul_scaled 

fn matrix_mul_scaled(a: &[Fixed; 6], b: &[Fixed; 6], scaling: i32) -> [Fixed; 6]

Simple fixed point matrix multiplication with a scaling factor.

Note: this transforms the translation component of b by the upper 2x2 of a. This matches the offset transform FreeType uses when concatenating the matrices from the top and font dicts.

See https://gitlab.freedesktop.org/freetype/freetype/-/blob/80a507a6b8e3d2906ad2c8ba69329bd2fb2a85ef/src/base/ftcalc.c#L719