referenceChart surface shader

A reference chart drawn on a surface, unlit: each point holds light its properties and its UV state, so a picture of the surface is measured against known input. The post-verification reference scenes (@builtin::scenes.postReference.*) are built from its materials (@builtin::materials.postReference.*).

pattern	Draws
0	A grey wedge: one column per whole stop from evMin to evMax, each middle grey (0.18) at that stop.
1	The 24 ColorChecker Classic patches, 6 x 4, each its published sRGB value read as linear reflectance.
2	A ramp from low at u = 0 to high at u = 1.
3	A Siemens star of frequency spokes, high on low.
4	A checker frequency cells across, low and high.
5	Focus bars: four rows of bar pairs, frequency pairs across the top row, doubling on each row below.

Every pattern's light is multiplied by color and gain. UV (0, 0) is the surface's top-left, as the front face of @builtin::meshes.cube maps it.