Change map to use key-value array for binary, integer, etc

Summary:
After this diff, we only use object form for string/enum keys.

Note that today both string and binary are TType::T_STRING. We need to pass type tag to `writeMapBegin` in order to distinguish them.

Reviewed By: iahs

Differential Revision: D95452478

fbshipit-source-id: 3b48c722c1571d65a0084f876f0f553c33ccd42f

Author: Mizuchi

third-party/thrift/src/thrift/lib/cpp2/op/detail/Encode.h

@@ -694,10 +694,17 @@ struct MapEncode {
   template <typename Protocol, typename T>
   uint32_t operator()(Protocol& prot, const T& map) const {
     uint32_t xfer = 0;
-    xfer += prot.writeMapBegin(
-        typeTagToTType<Key>,
-        typeTagToTType<Value>,
-        checked_container_size(map.size()));
+    if constexpr (requires {
+                    prot.template writeMapBegin<Key, Value>(std::int32_t{});
+                  }) {
+      xfer += prot.template writeMapBegin<Key, Value>(
+          checked_container_size(map.size()));
+    } else {
+      xfer += prot.writeMapBegin(
+          typeTagToTType<Key>,
+          typeTagToTType<Value>,
+          checked_container_size(map.size()));
+    }
 
     if constexpr (
         !folly::is_detected_v<