Implement loading multiple predefined transformations for GeographicCoordinateSystem

[terribletim]

CoordinateSystemFactory currently adopts a single default WGS84ConversionInfo per GeographicCoordinateSystem as defined in the WKT (eg SharpMap SpatialRefSys.xml)

It is not uncommon for a GCS to have several different known transformations and GeographicCoordinateSystem has obviously been built with this in mind by exposing properties NumConversionToWGS84 and GetWgs84ConversionInfo (see here).

It doesn't seem like this has ever been implemented and I am happy to contribute subject to further discussion / direction (realize this might not be the best time due to focus on supporting Net Standard, so no problems if people aren't available).

My initial questions are:

1. Does anyone have a XML document of datum transformations? I'm not familiar with transformation data available in PostGIS 2.0 database (used to generate SpatialRefSys.xml) but I am familiar with the EPSG dataset where each transformation has a unique ID and well-known name, along with From/To SRIDs, transformation type, and transformation parameters.
2. If XML is available, should it be included in SharpMap SpatialRefSys.xml, or separate XML document?
3. Implementation would require additional properties for transformation metadata (eg ID, name, transformation type) in addition to WGS84ConversionInfo. At this stage I would only be attempting Position Vector (ie 7 param) transformations, but if going to this effort then it would be sensible to consider future support for other transformation types.

Regards

Tim