[flang] Do not create HostAssoc symbols in derived type scopes

[klausler]

Summary

When needed due to a specification expression in a derived type,
the host association symbols should be created in the surrounding
subprogram's scope instead.

[PeteSteinfeld]

All builds, tests, and looks good.

flang/lib/Semantics/resolve-names.cpp

 Symbol &ScopeHandler::MakeSymbol(const SourceName &name, Attrs attrs) {
   return MakeSymbol(currScope(), name, attrs);
 }
 Symbol &ScopeHandler::MakeSymbol(const parser::Name &name, Attrs attrs) {
   return Resolve(name, MakeSymbol(name.source, attrs));
 }
 Symbol &ScopeHandler::MakeHostAssocSymbol(
     const parser::Name &name, const Symbol &hostSymbol) {
-  Symbol &symbol{MakeSymbol(name, HostAssocDetails{hostSymbol})};
+  Symbol &symbol{*NonDerivedTypeScope()
+                      .try_emplace(name.source, HostAssocDetails{hostSymbol})
+                      .first->second};
   name.symbol = &symbol;
   symbol.attrs() = hostSymbol.attrs(); // TODO: except PRIVATE, PUBLIC?
   symbol.flags() = hostSymbol.flags();
   return symbol;
 }
 Symbol &ScopeHandler::CopySymbol(const SourceName &name, const Symbol &symbol) {
   CHECK(!FindInScope(name));
   return MakeSymbol(currScope(), name, symbol.attrs());