[NF] handle discrete variability better

- if the type of component is discrete return discrete if
  is lower variability than the explicit component variability
- handle discrete builtin calls (String, Integer, pre, edge, change)

Belonging to [master]:
  - #2063

Compiler/NFFrontEnd/NFCall.mo

@@ -497,8 +497,32 @@ uniontype Call
   algorithm
     argtycall := typeNormalCall(call, info);
     (call , ty, variability) := matchTypedNormalCall(argtycall, info);
+    variability := match call
+      case TYPED_CALL()
+        then getBuiltinVariability(
+               variability,
+               Absyn.pathLastIdent(Function.nameConsiderBuiltin(call.fn)));
+      else variability;
+    end match;
   end typeMatchNormalCall;
 
+  function getBuiltinVariability
+  "@author: adrpo
+   some builtin function have specific variability,
+   handle that here, TODO FIXME: see if we need more"
+    input output Variability variability;
+    input String name;
+  algorithm
+    variability := match name
+      case "pre" then Variability.DISCRETE;
+      case "edge" then Variability.DISCRETE;
+      case "change" then Variability.DISCRETE;
+      case "String" then Variability.DISCRETE;
+      case "Integer" then Variability.DISCRETE;
+      else variability;
+    end match;
+  end getBuiltinVariability;
+
   function typeNormalCall
     input output Call call;
     input SourceInfo info;
@@ -546,7 +570,7 @@ uniontype Call
     CallAttributes ca;
     list<TypedArg> tyArgs;
   algorithm
-    (argtycall , ty, variability) := match argtycall
+    (argtycall, ty, variability) := match argtycall
       case ARG_TYPED_CALL() algorithm
 
         // Match the arguments with the expected ones.

Compiler/NFFrontEnd/NFComponent.mo

@@ -409,7 +409,12 @@ uniontype Component
     output Variability variability;
   algorithm
     variability := match component
-      case TYPED_COMPONENT(attributes = Attributes.ATTRIBUTES(variability = variability)) then variability;
+      // adrpo: select discrete if the type is discrete and explicit component variability > discrete
+      case TYPED_COMPONENT(attributes = Attributes.ATTRIBUTES(variability = variability))
+        then
+          if Type.isDiscrete(component.ty) and variability > Variability.DISCRETE
+          then Variability.DISCRETE
+          else variability;
       case TYPED_COMPONENT() guard Type.isDiscrete(component.ty) then Variability.DISCRETE;
       case UNTYPED_COMPONENT(attributes = Attributes.ATTRIBUTES(variability = variability)) then variability;
       case ITERATOR() then Variability.CONSTANT;