[flang] Fix crash in semantics after PDT instantiation

[klausler]

Summary

The code in semantics that reinitializes symbol table pointers in
the parse tree of a parameterized derived type prior to a new
instantiation of the type was processing the symbols of the
derived type instantiation scope in arbitrary address order,
which could fail if a reference to a type parameter inherited from
an ancestor type was processed prior to the parent component sequence.
Fix by instantiating components of PDT instantiations in declaration
order.

flang/lib/Semantics/type.cpp

if (PlumbPDTInstantiationDepth(&containingScope) > 100) {
     foldingContext.messages().Say(
         "Too many recursive parameterized derived type instantiations"_err_en_US);
   } else {
     InstantiateHelper{newScope}.InstantiateComponents(typeScope);
   }
 }
 
 void InstantiateHelper::InstantiateComponents(const Scope &fromScope) {
-  for (const auto &pair : fromScope) {
-    InstantiateComponent(*pair.second);
+  // Instantiate symbols in declaration order; this ensures that
+  // parent components and type parameters of ancestor types exist
+  // by the time that they're needed.
+  for (SymbolRef ref : fromScope.GetSymbols()) {
+    InstantiateComponent(*ref);
   }
   ComputeOffsets(context(), scope_);
 }
 
 // Walks a parsed expression to prepare it for (re)analysis;
 // clears out the typedExpr analysis results and re-resolves
 // symbol table pointers of type parameters.
 class ComponentInitResetHelper {
 public:
   explicit ComponentInitResetHelper(Scope &scope) : scope_{scope} {}
 
   template <typename A> bool Pre(const A &) { return true; }
 
   template <typename A> void Post(const A &x) {
     if constexpr (parser::HasTypedExpr<A>()) {
       x.typedExpr.Reset();
     }
   }
 
   void Post(const parser::Name &name) {
     if (name.symbol && name.symbol->has<TypeParamDetails>()) {
-      name.symbol = scope_.FindSymbol(name.source);
+      name.symbol = scope_.FindComponent(name.source);
     }
   }
 
 private:
   Scope &scope_;
 };
 
 void InstantiateHelper::InstantiateComponent(const Symbol &oldSymbol) {