Start implementing ray-casting.

This adds a QueryPipeline structure responsible for scene queries.
Currently this structure is able to perform a brute-force ray-cast.
This commit also includes the beginning of implementation of a SIMD-based acceleration structure which will be used for these scene queries in the future.

src_testbed/physx_backend.rs

@@ -196,7 +196,8 @@ impl PhysxWorld {
                     }
                 } else {
                     physx_sys::PxShapeFlags {
-                        mBits: physx_sys::PxShapeFlag::eSIMULATION_SHAPE as u8,
+                        mBits: physx_sys::PxShapeFlag::eSIMULATION_SHAPE as u8
+                            | physx_sys::PxShapeFlag::eSCENE_QUERY_SHAPE as u8,
                     }
                 };