feat: support lighting and shadows for scatter and mesh

[maartenbreddels]

This supersedes 80% of #341, supporing shadows with instances. I've left out the GUI parts, to avoid getting stuck on that, so we can merge this hopefully quickly:

import ipyvolume as ipv
import numpy as np
f = ipv.figure()
ipv.xyzlim(-4, 4)
ipv.zlim(-10, 10)
x = np.array([0.0, 1.5, 3.0], dtype=np.float32)
s = ipv.scatter(x, x, x, lighting_model='PHYSICAL', roughness=0.4, metalness=0.1, size=20);
l = ipv.light_directional(position=[0, 1.0, 0.5])
# # m = ipv.plot_plane('bottom')
k = 4.
h = -2.
tx = np.array([k, -k, -k, k])
tz = np.array([k, k, -k, -k])
ty = np.array([h, h, h, h])
tri = [(0, 1, 2), (0, 2, 3)]
p = ipv.plot_trisurf(x=tx, y=ty, z=tz, triangles=tri, lighting_model='PHYSICAL')

k = 1.75
h = 1.
tx = np.array([k, -k, -k, k])
tz = np.array([k, k, -k, -k])
ty = np.array([h, h, h, h])
tri = [(0, 1, 2), (0, 2, 3)]
p = ipv.plot_trisurf(x=tx, y=ty, z=tz, triangles=tri, lighting_model='PHYSICAL')

ipv.zlim(-4, 4)
ipv.show()

This gives me:

TODO:

• color is grey in physical mode
• lighting + default lighting mode is broken
• mesh shadows are broken
• several TODO

[maartenbreddels]

Basically my approach was to take the threejs shaders (vertex and fragment) and merge them into 1 shader, where the defines (AS_DEFAULT, AS_PHONG... , AS_DEPTH) decide which shader to execute.
the depth shader was needed to get the shadows to work with instancing for the scatter, and also property with the mesh.

[maartenbreddels]

Mesh shaders were broken, this is fixed now:

[maartenbreddels]

colors are fixed: