TopographicLineMaterial: Improvements

[gkjohnson]

• See if we can calculate height in the fragment shader based on the ellipsoid rather than interpolating in the vertex shader.
  • Try scaling the values
• Consider presenting elevation to at least the granularity of the current topo lines.
• ~Fix support for topo plugin shallow arguments~
• ~Ensure calculations for topo pixel spacing are correct (dpr isn't accounted for in margin?)~
• ~Add helper function for determining transition boundaries, line stride on CPU for info display.~
• ~Consider shifting the resolution value to a uniform rather than calculated.~
• ~Adjust the fade limit defaults for the globe so the carto and topo lines don't overlap.~
• ~Consider decreasing step size if the terrain has a low rate-of-change (fwidth of perpendicular values)?~ This will result in some odd spotty cases of topo lines.

Other

• Allow for more scalable precision elevation display. Ie because the elevation is clamped to 2 decimal places the precision of the displayed value diminishes further from the origin.
• Add dynamic line where the mouse is / highlight height
• Adjust fade transition distance for ortho camera (or near ortho cameras)
• Rename "topo" to "contour"
• Add middle line to improve readability.
• Remaining precision issues
  • Shift values to be relative to a nearby value so the interpolation is not happening on such small fields
• Consider controllable feature for adjusting the number of segments per stride - eg use 9 at the highest level for cartographic
• Consider other options
  • number of segments per emphasis line
  • ~thickness~

Related to #1086

[gkjohnson]

Add measurement tool:

• Add horizontal measurement
• Vertical elevation, contour markers
• Display lat / lon under mouse