[backtrace] add otSysRegisterCrashCallback to register crash callback function (#12552)

This commit adds `otSysRegisterCrashCallback` function which can be used
to register the callback function to be called when openthread crashes.

src/posix/platform/backtrace.cpp

@@ -40,10 +40,15 @@
 #include <string.h>
 #include <unistd.h>
 
+#include <openthread/openthread-system.h>
+
 #include "common/code_utils.hpp"
 #include "common/logging.hpp"
 
 #if OPENTHREAD_POSIX_CONFIG_BACKTRACE_ENABLE
+static otSysCrashCallback sCrashCallback = nullptr;
+
+void otSysRegisterCrashCallback(otSysCrashCallback aCallback) { sCrashCallback = aCallback; }
 #if OPENTHREAD_POSIX_CONFIG_ANDROID_ENABLE || defined(__GLIBC__)
 #if OPENTHREAD_POSIX_CONFIG_ANDROID_ENABLE
 #include <log/log.h>
@@ -156,6 +161,11 @@ static void signalCritical(int sig, siginfo_t *info, void *ucontext)
 
     otLogCritPlat("------------------ END OF CRASH ------------------");
 
+    if (sCrashCallback != nullptr)
+    {
+        sCrashCallback();
+    }
+
     resetSignalActions();
     raise(sig);
 }

src/posix/platform/include/openthread/openthread-system.h

@@ -330,6 +330,23 @@ void otSysTrelDeinit(void);
  */
 void otSysSetRcpRestorationEnabled(bool aEnabled);
 
+/**
+ * Represents a callback function to be called when openthread crashes.
+ *
+ * @note This callback is invoked from a signal handler context. The callback implementation must only use
+ *       async-signal-safe functions.
+ */
+typedef void (*otSysCrashCallback)(void);
+
+/**
+ * Registers the callback function to be called when openthread crashes.
+ *
+ * Requires `OPENTHREAD_POSIX_CONFIG_BACKTRACE_ENABLE`.
+ *
+ * @param[in] aCallback  The callback function.
+ */
+void otSysRegisterCrashCallback(otSysCrashCallback aCallback);
+
 #ifdef __cplusplus
 } // end of extern "C"
 #endif