Return information about an AstroCoords element stored in an Stc AST_GETSTCCOORD
If the coordinate system represented by the Stc has been changed since it was created (for instance, by changing its System attribute), then the sizes and positions in the returned KeyMap will reflect the change in coordinate system.
A null Object pointer (AST__NULL) will be returned if this function is invoked with STATUS set to an error value, or if it should fail for any reason.