Refactor: Isolate and abstract three.js related code.

[freezy]

This PR abstracts render-related code into an interface that can be implemented by other WebGL frameworks. The main goal is to be able to tree-shake non-used render code (and specially three.js) in case another WebGL framework is used.

Future candidates for render support are Babylon.js, PlayCanvas and maybe Google's Filament.

There are still a few quirks that probably will need to be resolved once support for another renderer is added:

• Playfield light meshes aren't stored as vertices in the VPX file. Currently we use three.js to extrude a 3D mesh out of a path. So unless we can rewrite this to generate vertices the whole light mesh generation is current part of the API and needs to be re-implemented for every framework
• Idem for the playfield itself, although Handle playfield mesh properly #49 will probably solve that.

[codecov]

Codecov Report

Merging #50 into master will increase coverage by 0.4%.
The diff coverage is 91.8%.

@@           Coverage Diff            @@
##           master     #50     +/-   ##
========================================
+ Coverage    90.2%   90.6%   +0.4%     
========================================
  Files         155     158      +3     
  Lines       10011    9938     -73     
  Branches     1156    1125     -31     
========================================
- Hits         9027    8998     -29     
+ Misses        610     570     -40     
+ Partials      374     370      -4

Impacted Files	Coverage Δ
lib/math/matrix3d.ts	97% <ø> (+1.6%)	⬆️
lib/vpt/primitive/primitive.ts	88.9% <ø> (ø)	⬆️
lib/vpt/mesh.ts	91.3% <ø> (+0.7%)	⬆️
lib/vpt/item-state.ts	100% <ø> (+40%)	⬆️
lib/vpt/light/light-data.ts	94.9% <ø> (-2.5%)	⬇️
lib/util/object-pool.ts	97% <ø> (+54.5%)	⬆️
lib/gltf/image.node.ts	64.5% <ø> (-2.6%)	⬇️
lib/vpt/rubber/rubber.ts	95.3% <ø> (ø)	⬆️
lib/vpt/item-data.ts	95.2% <ø> (ø)	⬆️
lib/vpt/light/light-mesh-generator.ts	100% <ø> (+2.1%)	⬆️
... and 39 more

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