Add ability to store and retrieve a list of MapBuffer

Summary:
Add ability to store and retrieve a list of MapBuffer as an entry of MapBuffer.

```
Example:

MapBuffer1
{
 key1: "test string",
 key2: MapBuffer2,
 key3: [MapBuffer3, MapBuffer4]
}
```

Changelog:
[General][Added] Add ability to store and retrieve a list of MapBuffer

Reviewed By: JoshuaGross

Differential Revision: D38460204

fbshipit-source-id: 3e721418be2dca6d5f15f665753844d6f531e31c

ReactCommon/react/renderer/mapbuffer/tests/MapBufferTest.cpp

@@ -6,6 +6,7 @@
  */
 
 #include <memory>
+#include <vector>
 
 #include <gtest/gtest.h>
 #include <react/renderer/mapbuffer/MapBuffer.h>
@@ -150,6 +151,30 @@ TEST(MapBufferTest, testMapEntries) {
   EXPECT_EQ(readMap2.getInt(1), 1234);
 }
 
+TEST(MapBufferTest, testMapListEntries) {
+  std::vector<MapBuffer> mapBufferList;
+  auto builder = MapBufferBuilder();
+  builder.putString(0, "This is a test");
+  builder.putInt(1, 1234);
+  mapBufferList.push_back(builder.build());
+
+  auto builder2 = MapBufferBuilder();
+  builder2.putInt(2, 4321);
+  builder2.putDouble(3, 908.1);
+  mapBufferList.push_back(builder2.build());
+
+  auto builder3 = MapBufferBuilder();
+  builder3.putMapBufferList(5, std::move(mapBufferList));
+  auto map = builder3.build();
+
+  std::vector<MapBuffer> mapBufferList2 = map.getMapBufferList(5);
+
+  EXPECT_EQ(mapBufferList2.size(), 2);
+  EXPECT_EQ(mapBufferList2[0].getString(0), "This is a test");
+  EXPECT_EQ(mapBufferList2[0].getInt(1), 1234);
+  EXPECT_EQ(mapBufferList2[1].getDouble(3), 908.1);
+}
+
 TEST(MapBufferTest, testMapRandomAccess) {
   auto builder = MapBufferBuilder();
   builder.putInt(1234, 4321);