ProjectTableMapping CRS input, `lon_lat_height` table EPSG:4979 & optimize `pyproj` vertical transformation

[JoostGevaert]

ProjectTableMapping CRS

Should have a single crs input that accepts one of:

• CompoundCRS
• (ProjectedCRS, VerticalCRS)
• HorizontalCRS
• 3D Geodetic CRS
• 2D Geodetic CRS

LonLatHeight table EPSG:4979 & optimize pyproj vertical transformation

Currently LonLatHeight uses WGS 84 + EGM2008 orthometric Height (EPSG:9518). This has to be changed to WGS 84 with ellipsoidal height (EPSG:4979) for at least two reasons:

1. 3D transformations between SRSes that use ellipsoidal heights are possible without geoid undulation grids. This is impossible with 3D SRSes that use orthometric heights.
2. WGS 84 with ellipsoidal height (EPSG:4979) is more commonly used by other apps. Software such as CesiumJS can handle WGS 84 with ellipsoidal height (EPSG:4979), but not WGS 84 + EGM2008 orthometric height (EPSG:9518).

The correct way to do vertical transformations:

1. Check whether PROJ-data has a geoid undulation grid available for the given vertical SRS.
2. Now there are 2 options:
   a. Yes => do the transformation using the geoid grid. In order to do so, PROJ needs to access the geoid grid from cdn.proj.org. Therefore, ensure that pyproj.network.set_network_enabled(active=True), see PROJ Network Settings.
   b. No => promote the 2D projected SRS to 3D .to_3d(). This adds the ellipsoidal height for that SRS to the SRS. See sketch below: