Support vertexColors for meshes via GeometryBasics.meta

[rdeits]

Example:

# Create a simple mesh with a single triangle
geometry = GeometryBasics.Mesh(
    [Point(0., 0, 0), Point(1., 0, 0), Point(1., 1, 0)],
    [NgonFace(1, 2, 3)])
# Wrap that mesh with metadata encoding the vertex colors
mesh_meta = meta(geometry, vertexColors=[RGB(1, 0, 0), RGB(0, 1, 0), RGB(0, 0, 1)])
# Create a Gouraud-shaded material with vertex coloring enabled
material = MeshLambertMaterial(vertexColors=true)
# Add it to the scene
setobject!(v[:vertex_color_mesh], mesh_meta, material)
settransform!(v[:vertex_color_mesh], Translation(1, -1.5, 0))

Result:

[codecov-commenter]

Codecov Report

Merging #183 into master will increase coverage by 0.21%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #183      +/-   ##
==========================================
+ Coverage   78.41%   78.62%   +0.21%     
==========================================
  Files          18       18              
  Lines         505      510       +5     
==========================================
+ Hits          396      401       +5     
  Misses        109      109              

Impacted Files	Coverage Δ
src/MeshCat.jl	80.00% <ø> (ø)
src/lowering.jl	96.05% <100.00%> (+0.27%)	:arrow_up:

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