Implement source debugging for interpreter and AOT (#769)

Implement source debugging feature for classic interpreter and AOT:
- use `cmake -DWAMR_BUILD_DEBUG_INTERP=1` to enable interpreter debugging
- use `cmake -DWAMR_BUILD_DEBUG_AOT=1` to enable AOT debugging

See doc/source_debugging.md for more details.

core/iwasm/libraries/debug-engine/packets.h

@@ -0,0 +1,22 @@
+/*
+ * Copyright (C) 2021 Ant Group.  All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+ */
+
+#ifndef PACKETS_H
+#define PACKETS_H
+
+#include <stdint.h>
+#include <unistd.h>
+#include "gdbserver.h"
+
+bool
+read_packet(WASMGDBServer *gdbserver);
+
+void
+write_packet(WASMGDBServer *gdbserver, const char *data);
+
+void
+inbuf_erase_head(WASMGDBServer *gdbserver, ssize_t end);
+
+#endif