Add: A group of classes imported from lib https://github.com/ixmilia/step under MIT license, representing all STEP AP203 geometry objects
Change: many change to classes from https://github.com/ixmilia/step to link data interfaces to those in StgSharp
Freeze: implementation to StgSharp EXPRESS interpreter about collextion operation and element define grammer
Signed-off-by: Nitload <YoumuLiu_NSI@whv0t.onmicrosoft.com>