Allow customizing CompactSubGeometry.

[player-03]

Most users likely don't need "secondary UVs", for instance, and could save memory by omitting them. Others might want to add a custom 4-length attribute (not fully implemented; you can define them but they'll be ignored).

Sample usage:

final vertexDefinition:VertexDefinition = new VertexDefinition([
	new AttributeDefinition("position", 3),
	new AttributeDefinition("UV", 2)
]);
final geometry:CompactSubGeometry = new CompactSubGeometry(vertexDefinition);

//Add geometry containing positions and UVs...

view.scene.addChild(new Mesh(geometry));

This sub-geometry allocates only 5 floats per vertex, instead of 13, massively reducing buffer size.

[player-03]

Oh, and I wrote this for Haxe 4.3+, so that's another reason it's still a draft.