ENH: snappyHexMesh multi-pass layer addition

Functionality to add/problem to solve

Add layers in snappyHexMesh one-by-one.

Target audience

Multi-layer generation on smooth surfaces

Proposal

Calculate the wanted amount of layers and distribution of thickness. Add layers one-by-one (still growing out from the bulk)

What does success look like, and how can we measure that?

Optionally add layers one-by-one. Compare to adding layers in one go (the default).