DeclContext: Fix iterator category

[HazardyKnusperkeks]

Summary

This amends 0cb7e7ca0c864e052bf49978f3bcd667c9e16930. (D91524)

The iterator category of lookup_iterator was changed, but here it stayed
hardcoded as random access. Found while trying to build Clazy.

[HazardyKnusperkeks]

Trigger build.

[v.g.vassilev]

Nice catch! Thanks!

clang/include/clang/AST/DeclBase.h

public:
   /// source.
   all_lookups_iterator noload_lookups_begin() const;
   all_lookups_iterator noload_lookups_end() const;
 
   struct udir_iterator;
 
   using udir_iterator_base =
       llvm::iterator_adaptor_base<udir_iterator, lookup_iterator,
-                                  std::random_access_iterator_tag,
+                                  typename lookup_iterator::iterator_category,
                                   UsingDirectiveDecl *>;
 
   struct udir_iterator : udir_iterator_base {
     udir_iterator(lookup_iterator I) : udir_iterator_base(I) {}
 
     UsingDirectiveDecl *operator*() const;
   };