[lldb][NFCI] Replace bespoke iterator check with std::next

[bulbazord]

Summary

The primary goal of this change is to change if (pair != *(--m_dict.end()))
to if (std::next(iter) != m_dict.end()). I was experimenting with
changing the underlying type of m_dict and found that this was an
issue. Specifically, it assumes that m_dict iterators are bidirectional.
This change should make it so we only need to assume m_dict iterators can move
forward.

[JDevlieghere]

LGTM 🚢

[fdeazeve]

Nice catch!

lldb/source/Utility/StructuredData.cpp

for (const auto &item_sp : m_items) {
     // Reset indentation level if it was incremented previously.
     if (should_indent)
       s.IndentLess();
   }
 }
 
 void StructuredData::Dictionary::GetDescription(lldb_private::Stream &s) const {
   size_t indentation_level = s.GetIndentLevel();
-  for (const auto &pair : m_dict) {
+  for (auto iter = m_dict.begin(); iter != m_dict.end(); iter++) {
     // Sanitize.
-    if (pair.first.IsNull() || pair.first.IsEmpty() || !pair.second)
+    if (iter->first.IsNull() || iter->first.IsEmpty() || !iter->second)
       continue;
 
     // Reset original indentation level.
     s.SetIndentLevel(indentation_level);
     s.Indent();
 
     // Print key.
-    s.Printf("%s:", pair.first.AsCString());
+    s.Printf("%s:", iter->first.AsCString());
 
     // Return to new line and increase indentation if value is record type.
     // Otherwise add spacing.
-    bool should_indent = IsRecordType(pair.second);
+    bool should_indent = IsRecordType(iter->second);
     if (should_indent) {
       s.EOL();
       s.IndentMore();
     } else {
       s.PutChar(' ');
     }
 
     // Print value and new line if now last pair.
-    pair.second->GetDescription(s);
-    if (pair != *(--m_dict.end()))
+    iter->second->GetDescription(s);
+    if (std::next(iter) != m_dict.end())
       s.EOL();
 
     // Reset indentation level if it was incremented previously.
     if (should_indent)
       s.IndentLess();
   }
 }
 
 void StructuredData::Null::GetDescription(lldb_private::Stream &s) const {
   s.Printf("NULL");
 }
 
 void StructuredData::Generic::GetDescription(lldb_private::Stream &s) const {
   s.Printf("%p", m_object);
 }