Create a three-dimensional convex hull for a set of points.

Input parameters:

1. Pt → Points to include in the hull.
2. W → Whether the hull mesh shares vertices between facets (welded) or keeps each facet's vertices separate (unwelded).
   •  True → Welded
   • False → Unwelded

Output parameters:

1. Ms → Mesh representing the convex hull.
2. Ix → Indices of the input points used as vertices on the hull.