MVTAnnotationsPlugin: Add raycasting improvements, customization

[gkjohnson]

Related to #1600
Related to #449

• Add userdata.tile field to objects
• MVTAnnotationsDriver: add an optional "settle raycast" function
• MVTAnnotations: Remove hard coded earth constants used during line parsing
• MVTAnnotations: Prioritize high LoD tiles for settling

TODO

• Create issue for the following:
• The new prioritization does not work for additive tiles
• Consider centralizing a mechanism that picks the "best" hit
  • Prioritize visible over active to avoid "data cliffs"?
  • Prioritize highest LoD? How to deal with additive?