Add getVertices to ConvexShape

[xiejiangzhi]

No description provided.

[bjornbytes]

I feel like the API here is too opinionated/specific.

• It uses a hardcoded data format. So if someone wants something slightly different (smooth normals, packed normals, extra attributes), then they have to give up and rewrite it in Lua.
• The data it returns is already exposed by :getPoint and :getFace, so it's already possible to write this in Lua.
• There aren't really places in the existing API where we return a vertex blob unless you count ModelData:getBlob.

For now I'd recommend moving this code to Lua or keeping it on a fork.

I do still think the current API for the convex hull data is a little clunky. Adding :getPoints may help, for people that want all the points in a table anyway. Or it could return multiple returns like LÖVE's PolygonShape:getPoints does, but I'm not sure what the max number of points in the hull is, so it might be too many return values.