[lldb/Utility] Make `StructuredData::Dictionary::GetKeys` return an `Array`

[mib]

Summary

This patch changes StructuredData::Dictionary::GetKeys return type
from an StructuredData::ObjectSP to a StructuredData::ArraySP.

The function already stored the keys in an array but implicitely upcasted
it to an ObjectSP, which required the user to convert it again to a
Array object to access each element.

Since we know the keys should be held by an iterable container, it makes
more sense to return the allocated ArraySP as-is.

Signed-off-by: Med Ismail Bennani <[e-mail]>

[JDevlieghere]

Makes sense. LGTM

lldb/include/lldb/Utility/StructuredData.h

public:
     void ForEach(std::function<bool(ConstString key, Object *object)> const
                      &callback) const {
       for (const auto &pair : m_dict) {
         if (!callback(pair.first, pair.second.get()))
           break;
       }
     }
 
-    ObjectSP GetKeys() const {
-      auto object_sp = std::make_shared<Array>();
+    ArraySP GetKeys() const {
+      auto array_sp = std::make_shared<Array>();
       collection::const_iterator iter;
       for (iter = m_dict.begin(); iter != m_dict.end(); ++iter) {
         auto key_object_sp = std::make_shared<String>();
         key_object_sp->SetValue(iter->first.AsCString());
-        object_sp->Push(key_object_sp);
+        array_sp->Push(key_object_sp);
       }
-      return object_sp;
+      return array_sp;
     }
 
     ObjectSP GetValueForKey(llvm::StringRef key) const {
       ObjectSP value_sp;
       if (!key.empty()) {
         ConstString key_cs(key);
         collection::const_iterator iter = m_dict.find(key_cs);
         if (iter != m_dict.end())