0023787: Eliminate trivial type conversion warnings in MSVC

Explicit type cast added in conversions from double to float in PrsMgr, Select3D, StdPrs, Visual3d, and Voxel.
Minor corrections in ShapeProcess and TCollection.
In Visual3d_ViewManager::ConvertCoord...(), output is initialized by zeros instead of RealLast() in case of failure.
In XmlMXCAFDoc, material density is correctly converted to string when writing to Xml.

src/Voxel/Voxel_Reader.cxx

@@ -359,7 +359,7 @@ Standard_Boolean Voxel_Reader::ReadFloatAsciiVoxels(const TCollection_ExtendedSt
 	  return Standard_False;
 	}
       }
-      value = Atof(line);
+      value = (Standard_ShortReal)Atof(line);
 
       // Set value
       if (!((Standard_ShortReal**)((Voxel_DS*)myFloatVoxels)->myData)[i1])