CMake: Move mbedtls stub headers to the mbedtls doubles dir

Previously all the mbedtls stubs headers under mbed-stubs-headers,
so this PR move all mbedtls stubs headers under
mbedtls/tests/UNITTESTS/double directory and update CMake to include
stubs headers into mbed-stubs-mbedtls library to make mbedtls stubs
to be self-contained.
Made a copy of mbedtls_stub.h and add it into mbed-stubs-mbedtls as
previously this file gets referred from
connectivity/nanostack/coap-service/test/coap-service/unittest/stub/mbedtls_stub.h
and problem is nanostack unit test is not maintained as part of mbed os unit tests.

Author: rajkan01

connectivity/mbedtls/tests/UNITTESTS/doubles/CMakeLists.txt

@@ -11,6 +11,11 @@ target_include_directories(mbed-headers-mbedtls
 
 add_library(mbed-stubs-mbedtls)
 
+target_include_directories(mbed-stubs-mbedtls
+    PUBLIC
+        .
+)
+
 target_sources(mbed-stubs-mbedtls
     PRIVATE
         aes_stub.c

UNITTESTS/stubs/aes_stub.h renamed to connectivity/mbedtls/tests/UNITTESTS/doubles/aes_stub.h

@@ -0,0 +1,54 @@
+/*
+ * Copyright (c) 2015-2017, 2019-2020, Pelion and affiliates.
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#ifndef MBEDTLS_STUB_H
+#define MBEDTLS_STUB_H
+
+#define MBEDTLS_SSL_EXPORT_KEYS
+
+#include <inttypes.h>
+#include <stdbool.h>
+#include "mbedtls/platform.h"
+#include "mbedtls/ssl.h"
+#include "mbedtls/ctr_drbg.h"
+#include "mbedtls/hmac_drbg.h"
+#include "mbedtls/x509_crt.h"
+#include "mbedtls/sha256.h"
+#include "mbedtls/entropy.h"
+#include "mbedtls/pk.h"
+#include "mbedtls/platform.h"
+#include "mbedtls/md.h"
+
+
+#define HANDSHAKE_FINISHED_VALUE 8888
+#define HANDSHAKE_FINISHED_VALUE_RETURN_ZERO 8889
+
+typedef struct {
+    int crt_expected_int;
+    bool useCounter;
+    int counter;
+    int retArray[20];
+    int expected_int;
+    uint32_t uint32_value;
+    bool invalidate_timer;
+    void *cookie_obj;
+    unsigned char cookie_value[8];
+    size_t cookie_len;
+} mbedtls_stub_def;
+
+extern mbedtls_stub_def mbedtls_stub;
+
+#endif // MBEDTLS_STUB_H