Fabric: toString methods were moved into DebugStringConvertible with an implementation in .cpp file

Summary:
They need to be in DebugStringConvertible because it depends on they (and because `debugStringConvertibleUtils` depends on `DebugStringConvertible`).
We also moved they implementation to cpp file to avoid leaking Folly's features to consumer namespace.

Reviewed By: mdvacca

Differential Revision: D14715080

fbshipit-source-id: 7277e17b39a14a2d7ba7e5a9b44a70178feb1045

ReactCommon/fabric/debug/DebugStringConvertible.cpp

@@ -7,6 +7,9 @@
 
 #include "DebugStringConvertible.h"
 
+#include <folly/Conv.h>
+#include <folly/Format.h>
+
 namespace facebook {
 namespace react {
 
@@ -107,6 +110,28 @@ SharedDebugStringConvertibleList DebugStringConvertible::getDebugProps() const {
   return SharedDebugStringConvertibleList();
 }
 
+/*
+ * `toString`-family implementation.
+ */
+std::string toString(std::string const &value) {
+  return value;
+}
+std::string toString(int const &value) {
+  return folly::to<std::string>(value);
+}
+std::string toString(bool const &value) {
+  return folly::to<std::string>(value);
+}
+std::string toString(float const &value) {
+  return folly::to<std::string>(value);
+}
+std::string toString(double const &value) {
+  return folly::to<std::string>(value);
+}
+std::string toString(void const *value) {
+  return folly::sformat("0x{0:016x}", reinterpret_cast<size_t>(value));
+}
+
 #endif
 
 } // namespace react