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/utils.c

@@ -0,0 +1,45 @@
+/*
+ * Copyright (C) 2021 Ant Group.  All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+ */
+
+#include "utils.h"
+
+int
+hex(char ch)
+{
+    if ((ch >= 'a') && (ch <= 'f'))
+        return (ch - 'a' + 10);
+    if ((ch >= '0') && (ch <= '9'))
+        return (ch - '0');
+    if ((ch >= 'A') && (ch <= 'F'))
+        return (ch - 'A' + 10);
+    return (-1);
+}
+
+char *
+mem2hex(char *mem, char *buf, int count)
+{
+    unsigned char ch;
+
+    for (int i = 0; i < count; i++) {
+        ch = *(mem++);
+        *buf++ = hexchars[ch >> 4];
+        *buf++ = hexchars[ch % 16];
+    }
+    *buf = 0;
+    return (buf);
+}
+
+char *
+hex2mem(char *buf, char *mem, int count)
+{
+    unsigned char ch;
+
+    for (int i = 0; i < count; i++) {
+        ch = hex(*buf++) << 4;
+        ch = ch + hex(*buf++);
+        *(mem++) = ch;
+    }
+    return (mem);
+}