espnet: WIP support for on-chip WiFi on an ESP32C3

Work in progress. Does not work yet.

Some notes:

  - This requires some changes to TinyGo, look at the espnet branch.
  - The  next step is probably defining all the functions in
    g_wifi_osi_funcs (see espnet.c). Right now it hangs in
    esp_wifi_init_internal, probably a NULL pointer dereference.
  - This is only for the ESP32-C3. This will require some work to work
    on other chips from Espressif.

espnet/espnet.h

@@ -0,0 +1,4 @@
+#include <stdbool.h>
+#include "esp_private/wifi_os_adapter.h"
+
+extern wifi_osi_funcs_t g_wifi_osi_funcs;