Mesh sizing for sub sections of entities

When rounding an entity small sections with tight curvature can be generated that are separate to those of any enclosing entity. It would be good to be able to apply a sizing field just on the curved segments without affecting surrounding size fields. This technique could apply to curved entities, but also to bridges where the entity specific size could come from the bridge height itself.

Using this technique it ought also to be possible to make a dial for resolving curves on their own, separate from any surrounding entity. As a `CurvilinearRegion` is rendered, for any curved section could establish a size field to achieve a given geometric discretization error. The parameters for this sizing would come from the radius of the curvature, and then could bisect the length of the given curve until the segment length was less than the size field.

This would give the ability to do something like "nsegments per curve" or some other similar interface. Possibly even not exposing this option to users, and performing it automatically based on a curvature tolerance combined with the rounding radius.