Implement post-MVP features and native stack overflow check (#243)

Implement native thread stack overflow check
Implement post-MVP: Non-trapping float-to-int conversions
Implement post-MVP: Sign-extension operators
Enhance WASM loader checks

core/shared/platform/zephyr/zephyr_thread.c

@@ -444,3 +444,13 @@ int os_cond_signal(korp_cond *cond)
     return BHT_OK;
 }
 
+uint8 *os_thread_get_stack_boundary()
+{
+#if defined(CONFIG_THREAD_STACK_INFO)
+    korp_tid thread = k_current_get();
+    return (uint8*)thread->stack_info.start;
+#else
+    return NULL;
+#endif
+}
+