Support New ISIS PROJ4 String Mapping Groups

[acpaquette]

Feature description

After PROJ support was added to ISIS, there is a new mapping group that ISIS produces for PROJ string based projections. Here is an example of a PROJ mapping group:

Group = Mapping
  TargetName         = Mars
  ProjectionName     = IProj
  EquatorialRadius   = 3396190.0 <meters>
  PolarRadius        = 3396190.0 <meters>
  LatitudeType       = Planetographic
  LongitudeDirection = PositiveEast
  LongitudeDomain    = 180 <degrees>
  PixelResolution    = 4.8858749590614 <meters/pixel>
  Scale              = 12131.84905876 <pixels/degree>
  UpperLeftCornerX   = -10380549.481522 <meters>
  UpperLeftCornerY   = -4601028.4489481 <meters>
  MinimumLatitude    = -80.16734138218
  MaximumLatitude    = -77.62218369032
  MinimumLongitude   = -175.12611096354
  MaximumLongitude   = -169.78279917128
  ProjStr            = "+proj=eqc +lat_ts=0 +lat_0=0 +lon_0=0 +x_0=0 +y_0=0
                        +a=3396190 +b=3396190 +units=m +no_defs +type=crs"
End_Group

The above group is built off of the proj string provided under "ProjStr" and is named "IProj"

In GDAL, one would only need add the "ProjStr" to the projected product to get the projection and create the geotransform from the pixel resolution and upper left corner x/y.

Additional context

No response