ESP IDF fixes (#927)

Various fixes and beautifications coordinated with @1c3t3a,
fixes 2 of the 3 all remaining issues from #892:
- enable to os_mmap executable memory
- fix os_malloc/os_realloc/os_free issues
- implement os_thread_get_stack_boundary
- add build scripts to include with esp-idf to use wamr as
  an ESP-IDF component
- update sample and document

product-mini/platforms/esp-idf/build_and_run.sh

@@ -0,0 +1,33 @@
+#!/bin/bash -e
+
+# Copyright (C) 2019-21 Intel Corporation and others.  All rights reserved.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+ESP32_TARGET="esp32"
+ESP32C3_TARGET="esp32c3"
+
+usage ()
+{
+        echo "USAGE:"
+        echo "$0 $ESP32_TARGET|$ESP32C3_TARGET"
+        echo "Example:"
+        echo "        $0 $ESP32_TARGET"
+        echo "        $0 $ESP32C3_TARGET"
+        exit 1
+}
+
+if [ $# != 1 ] ; then
+        usage
+fi
+
+TARGET=$1
+
+if [[ -z "${WAMR_PATH}" ]]; then
+        export WAMR_PATH=$PWD/../../..
+fi
+
+rm -rf build
+idf.py set-target $TARGET
+idf.py build
+idf.py flash
+