[api] remove UART from in cli/ncp API (#6243)

This commit removes application library CLI/NCP dependency on platform
layer UART APIs. Instead, application layer provides callbacks sending
CLI/NCP data.

With this change, platforms with native support for formatted output
can simply implement the CLI output callback with something like
`vprintf()`.

tests/fuzz/cli_received.cpp

@@ -0,0 +1,106 @@
+/*
+ *  Copyright (c) 2019, The OpenThread Authors.
+ *  All rights reserved.
+ *
+ *  Redistribution and use in source and binary forms, with or without
+ *  modification, are permitted provided that the following conditions are met:
+ *  1. Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ *  2. Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *  3. Neither the name of the copyright holder nor the
+ *     names of its contributors may be used to endorse or promote products
+ *     derived from this software without specific prior written permission.
+ *
+ *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ *  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ *  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ *  ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ *  LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ *  CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ *  SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ *  INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ *  CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ *  ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ *  POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#define MAX_ITERATIONS 100
+
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <openthread/cli.h>
+#include <openthread/instance.h>
+#include <openthread/ip6.h>
+#include <openthread/link.h>
+#include <openthread/tasklet.h>
+#include <openthread/thread.h>
+#include <openthread/thread_ftd.h>
+
+#include "fuzzer_platform.h"
+#include "common/code_utils.hpp"
+
+static int CliOutput(void *aContext, const char *aFormat, va_list aArguments)
+{
+    OT_UNUSED_VARIABLE(aContext);
+    OT_UNUSED_VARIABLE(aFormat);
+    OT_UNUSED_VARIABLE(aArguments);
+
+    return vsnprintf(nullptr, 0, aFormat, aArguments);
+}
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size)
+{
+    const otPanId panId = 0xdead;
+
+    otInstance *instance = nullptr;
+    uint8_t *   buf      = nullptr;
+
+    VerifyOrExit(size <= 65536);
+
+    FuzzerPlatformInit();
+
+    instance = otInstanceInitSingle();
+    otCliInit(instance, CliOutput, nullptr);
+    IgnoreError(otLinkSetPanId(instance, panId));
+    IgnoreError(otIp6SetEnabled(instance, true));
+    IgnoreError(otThreadSetEnabled(instance, true));
+    IgnoreError(otThreadBecomeLeader(instance));
+
+    buf = static_cast<uint8_t *>(malloc(size + 1));
+
+    memcpy(buf, data, size);
+    buf[size] = '\0';
+
+    otCliInputLine(reinterpret_cast<char *>(buf));
+
+    VerifyOrExit(!FuzzerPlatformResetWasRequested());
+
+    for (int i = 0; i < MAX_ITERATIONS; i++)
+    {
+        while (otTaskletsArePending(instance))
+        {
+            otTaskletsProcess(instance);
+        }
+
+        FuzzerPlatformProcess(instance);
+    }
+
+exit:
+
+    if (buf != nullptr)
+    {
+        free(buf);
+    }
+
+    if (instance != nullptr)
+    {
+        otInstanceFinalize(instance);
+    }
+
+    return 0;
+}