TilesRenderer: Add support for dynamic vertex animation, bounding volume adjustments

[gkjohnson]

If users make changs to the meshes - either via shader or via geometry (eg the flattening plugin) then the bounding hierarchy becomes out of sync and animations will not work. We should support updating tile geometry and updating bounds for traversal dynamically.

Some open questions / questions:

• Should we fire events for dynamic geometry or bounds updates so other plugins can be aware?
• Should we use a custom bounding box intersection function override via plugin?
• Or a margin system?
• Do we need a function to reset bounds back to their original state? Should we bookkeep the overridden bounds vs the originals?
• Should we have some helper function for adjust them?
• Do we need a "dirty" flag for the bounds so we only update the during traversal?

[gkjohnson]

Related to #1691 - the terrain rgb plugin allows for adjusting the height scale of the mesh, which implicitly updates all tile bounds and is slow. A method for scaling the tile bounds as-needed may be best. Or for performing custom bounds intersections that can account for the margins etc.