0027342: STEP - support C++ streams for import / export

- STEP low-level parser is converted to C++; required minimal version of flex is elevated to 2.5.37.
- Added possibility to import STEP from stream, see new method XSControl_Reader::ReadStream() (now implemented in STEP only).
- Parsers ported to win_flex_bison 2.5.23 (flex 2.6.4, bison 3.7.1)
- Added support of C++ flex and bison scanners in in CMake scripts
- Some code clean-up in StepFile and around (unused files and functions are eliminated)
- Option to read from stream is added in DRAW command testreadstep for testing ReadStream() function
- Added test bugs step bug27342

src/StepSelect/StepSelect_WorkLibrary.hxx

@@ -55,7 +55,15 @@ public:
   //! or lets <mod> "Null" in case of Error
   //! Returns 0 if OK, 1 if Read Error, -1 if File not opened
   Standard_EXPORT Standard_Integer ReadFile (const Standard_CString name, Handle(Interface_InterfaceModel)& model, const Handle(Interface_Protocol)& protocol) const Standard_OVERRIDE;
-  
+
+  //! Reads a STEP File from stream and returns a STEP Model (into <mod>),
+  //! or lets <mod> "Null" in case of Error
+  //! Returns 0 if OK, 1 if Read Error, -1 if File not opened
+  Standard_EXPORT Standard_Integer ReadStream(const Standard_CString theName,
+                                              std::istream& theIStream, 
+                                              Handle(Interface_InterfaceModel)& model,
+                                              const Handle(Interface_Protocol)& protocol) const Standard_OVERRIDE;
+
   //! Writes a File from a STEP Model
   //! Returns False (and writes no file) if <ctx> does not bring a
   //! STEP Model