Support InstancedMesh for LayoutComponents

[kalegd]

Initial thoughts

• Support a new parameter called instanced
• If instanced is true, then all components under the same parent with the same geometry will be instanced
• All instanced components will use MeshBasicMaterial with a white color, using InstancedMesh.setColorAt() to configure color
• Parents control the instances, when a child is added or removed, they are supplied with an instance or have it taken away
• We can have a global repository of geometries, and normalize geometry dimensions and then update the scale of the instanced mesh to provide the correct size

[kalegd]

Normalizing geometry dimensions is something I'll save for the future I think. Let's just start with everything else and see how that turns out first

Additional thing to think about, say we have a a couple of spans that all have the same internal structure of buttons and whatnot. Since the buttons all have the same offsets, they should be part of the same instanced mesh as long as the spans don't have their own overflow clipping planes. Otherwise each span is needlessly creating an instanced mesh for the buttons despite them all being the same. TLDR is that instead of the parent managing the instanced mesh, it should the the nearest ancestor with overflow clipping planes