Inconsistent definitions of feature ID

[Ralith]

In some places, parry uses the FeatureId enum, but TrackedContent uses a plain u32 for its feature IDs. This is also easily confused with the subshape u32s in ContactManifold, which identify logical shapes but not individual geometric features of a single shape (i.e. not necessarily a specific face, edge, or vertex). It's also unclear whether feature IDs in contact manifolds are scoped to shapes or subshapes, whereas FeatureIds necessarily must be shape-scoped since they're e.g. returned by PointQuery.

See also Discord discussion. Opening an issue for tracking purposes.