Implement function.toString operation (#4752)

May increase the memory consumtpion heavily.

JerryScript-DCO-1.0-Signed-off-by: Zoltan Herczeg zherczeg.u-szeged@partner.samsung.com

jerry-core/include/jerryscript-snapshot.h

@@ -30,7 +30,7 @@ extern "C"
 /**
  * Jerry snapshot format version.
  */
-#define JERRY_SNAPSHOT_VERSION (67u)
+#define JERRY_SNAPSHOT_VERSION (68u)
 
 /**
  * Flags for jerry_generate_snapshot and jerry_generate_function_snapshot.

jerry-core/include/jerryscript-types.h

@@ -112,6 +112,7 @@ typedef enum
   JERRY_FEATURE_PROMISE_CALLBACK, /**< Promise callback support */
   JERRY_FEATURE_MODULE, /**< Module support */
   JERRY_FEATURE_WEAKREF, /**< WeakRef support */
+  JERRY_FEATURE_FUNCTION_TO_STRING, /**< function toString support */
   JERRY_FEATURE__COUNT /**< number of features. NOTE: must be at the end of the list */
 } jerry_feature_t;