rcConfig Improvements

[grahamboree]

The values width and height are generally derived from other config values, but they're part of rcConfig which implies that they're meant to be user inputs to the rasterization process and should be set before creating the heightfield.

When building using the solo mesh process, the values width and height are derived from cs and bmin/bmax using rcCalcGridSize.

When building tile meshes, these values are simply defined as m_cfg.tileSize + m_cfg.borderSize*2.

These should just be computed from the other config values at the point they're needed.

Simple naming improvements

height: this is the z-axis size of the rasterized area. In every other case "height" refers to the y axis (e.g. ch) so this should be changed to something like depth
cs : rename to cellSize
ch: rename to cellHeight

🚨 These changes will create breaking API changes. We should be very deliberate about our release process for incorporating breaking API changes like this.