[NF] Variability fixes and other improvements.

- Replaced EquationScope, ClassScope and ExpOrigin with new ExpOrigin
  bitfield.
- Removed Component.Attributes.DEFAULT and Class.Attributes.DEFAULT,
  constants work equally well to save memory and simplifies the code.
- Set variables with no variability prefix and discrete type to be
  discrete so e.g. pre() works correctly.
- Fixed variability of many builtin functions.
- Fixed variability of relations with regards to noEvent.
- Fixed variability of expressions in when-clauses.
- Fixed typing of noEvent.
- Added check that time, pre, edge and change isn't used in a
  function context.
- Fixed handling of size on subscripted expressions.
- Moved handling of end to typing of subscripts, since the old handling
  relied upon ExpOrigin being a uniontype with subscript information.
- Improved handling of end to generate appropriate size expressions when
  the size of the dimension is unknown.
- Adapted the parenthesization algorithm from Dump to
  NFExpression.toString to get rid of extraneous parentheses in error
  messages.
- Fixed flattening of if-equations so the bodies of the branches aren't
  in reverse order compared with the conditions (oops...).

Belonging to [master]:
  - OpenModelica/OMCompiler#2069
  - OpenModelica/OpenModelica-testsuite#801

Compiler/NFFrontEnd/NFBuiltinFuncs.mo

@@ -60,39 +60,39 @@ constant SCode.Element DUMMY_ELEMENT = SCode.COMPONENT("dummy",
 
 // Default Integer parameter.
 constant Component INT_COMPONENT = Component.TYPED_COMPONENT(NFInstNode.EMPTY_NODE(),
-  Type.INTEGER(), Binding.UNBOUND(), Binding.UNBOUND(), Component.Attributes.DEFAULT(), Absyn.dummyInfo);
+  Type.INTEGER(), Binding.UNBOUND(), Binding.UNBOUND(), NFComponent.DEFAULT_ATTR, Absyn.dummyInfo);
 
 constant InstNode INT_PARAM = InstNode.COMPONENT_NODE("i",
   Visibility.PUBLIC,
   Pointer.createImmutable(INT_COMPONENT), 0, InstNode.EMPTY_NODE());
 
 // Default Real parameter.
 constant Component REAL_COMPONENT = Component.TYPED_COMPONENT(NFInstNode.EMPTY_NODE(),
-  Type.REAL(), Binding.UNBOUND(), Binding.UNBOUND(), Component.Attributes.DEFAULT(), Absyn.dummyInfo);
+  Type.REAL(), Binding.UNBOUND(), Binding.UNBOUND(), NFComponent.DEFAULT_ATTR, Absyn.dummyInfo);
 
 constant InstNode REAL_PARAM = InstNode.COMPONENT_NODE("r",
   Visibility.PUBLIC,
   Pointer.createImmutable(REAL_COMPONENT), 0, InstNode.EMPTY_NODE());
 
 // Default Boolean parameter.
 constant Component BOOL_COMPONENT = Component.TYPED_COMPONENT(NFInstNode.EMPTY_NODE(),
-  Type.BOOLEAN(), Binding.UNBOUND(), Binding.UNBOUND(), Component.Attributes.DEFAULT(), Absyn.dummyInfo);
+  Type.BOOLEAN(), Binding.UNBOUND(), Binding.UNBOUND(), NFComponent.DEFAULT_ATTR, Absyn.dummyInfo);
 
 constant InstNode BOOL_PARAM = InstNode.COMPONENT_NODE("b",
   Visibility.PUBLIC,
   Pointer.createImmutable(BOOL_COMPONENT), 0, InstNode.EMPTY_NODE());
 
 // Default String parameter.
 constant Component STRING_COMPONENT = Component.TYPED_COMPONENT(NFInstNode.EMPTY_NODE(),
-  Type.STRING(), Binding.UNBOUND(), Binding.UNBOUND(), Component.Attributes.DEFAULT(), Absyn.dummyInfo);
+  Type.STRING(), Binding.UNBOUND(), Binding.UNBOUND(), NFComponent.DEFAULT_ATTR, Absyn.dummyInfo);
 
 constant InstNode STRING_PARAM = InstNode.COMPONENT_NODE("s",
   Visibility.PUBLIC,
   Pointer.createImmutable(STRING_COMPONENT), 0, InstNode.EMPTY_NODE());
 
 // Default enumeration(:) parameter.
 constant Component ENUM_COMPONENT = Component.TYPED_COMPONENT(NFInstNode.EMPTY_NODE(),
-  Type.ENUMERATION_ANY(), Binding.UNBOUND(), Binding.UNBOUND(), Component.Attributes.DEFAULT(), Absyn.dummyInfo);
+  Type.ENUMERATION_ANY(), Binding.UNBOUND(), Binding.UNBOUND(), NFComponent.DEFAULT_ATTR, Absyn.dummyInfo);
 
 constant InstNode ENUM_PARAM = InstNode.COMPONENT_NODE("e",
   Visibility.PUBLIC,