[bscubed]

Adds VideoScaler::set_ycbcr_range() so callers can get limited (narrow) range YCbCr out of the scaler, next to the existing set_ycbcr_chroma_midpoint(). Full range stays the default, so existing output is unchanged.

For VK_SAMPLER_YCBCR_RANGE_ITU_NARROW at bit depth n, the luma row is scaled by 219 * 2^(n-8) / (2^n - 1) with offset 16 * 2^(n-8) / (2^n - 1), and the chroma rows by 224 * 2^(n-8) / (2^n - 1). The chroma midpoint still comes from set_ycbcr_chroma_midpoint(). Only the UBO matrix changes, so the scaler shader (and pyrowave's pre-generated slangmosh_scaler.hpp) is untouched.

Needed for Themaister/pyrowave#25 and Themaister/pyrowave#24.

[Themaister]

Painful that limited YCbCr needs to be supported, but at least it doesn't have to touch the shaders.