Consolidate JSON, JSONParseResults and JSONParser into JSON

Renames JSON.parse_string() to parse()
Renames JSON.decode_data() to stringify()

modules/mono/csharp_script.cpp

@@ -38,7 +38,6 @@
 #include "core/debugger/engine_debugger.h"
 #include "core/debugger/script_debugger.h"
 #include "core/io/file_access.h"
-#include "core/io/json.h"
 #include "core/os/mutex.h"
 #include "core/os/os.h"
 #include "core/os/thread.h"