Improve mesh grooming robustness with integrity checking and repair capability

[akenmorris]

The mesh grooming pipeline can produce or propagate invalid meshes (degenerate triangles, non-manifold edges, disconnected components) without detection, leading to failures or incorrect results in downstream optimization.

Specific issues:

• vtkFillHolesFilter can create zero-area triangles that cause problems later
• extractLargestComponent turns out to be a poor approach. It is basically required for many steps as part of cleaning, so there's no reason to expose it as an option.

[akenmorris]

Closed with #2478