Add (unsupported) BTstack Arduino library (earlephilhower#1305)

The BTstack driver includes a basic Arduino library as part of the ports
directory.

Author: earlephilhower

libraries/BTstack/README.rp2040

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+This is the BTstack ports/arduino library, with compile errors fixed only.

libraries/BTstack/examples/ANCS/ANCS.ino

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+#include <BTstack.h>
+#include <stdio.h>
+#include "ble/att_server.h"
+#include "ble/gatt_client.h"
+#include "ble/gatt-service/ancs_client.h"
+#include "ble/sm.h"
+#include "btstack_event.h"
+#include <SPI.h>
+
+/*
+   EXAMPLE_START(ANCS): ANCS Client
+*/
+
+/*
+   @section Advertisement
+   @text An ANCS Client needs to include the ANCS UUID in its advertisement to
+   get recognized by iOS
+*/
+
+/* LISTING_START(ANCSAdvertisement): ANCS Advertisement */
+const uint8_t adv_data[] = {
+  // Flags general discoverable
+  0x02, 0x01, 0x02,
+  // Name
+  0x05, 0x09, 'A', 'N', 'C', 'S',
+  // Service Solicitation, 128-bit UUIDs - ANCS (little endian)
+  0x11, 0x15, 0xD0, 0x00, 0x2D, 0x12, 0x1E, 0x4B, 0x0F, 0xA4, 0x99, 0x4E, 0xCE, 0xB5, 0x31, 0xF4, 0x05, 0x79
+};
+/* LISTING_END(ANCSAdvertisement): ANCS Advertisement */
+
+/*
+   @section Setup
+
+   @text In the setup, the LE Security Manager is configured to accept pairing requests.
+   Then, the ANCS Client library is initialized and and ancs_callback registered.
+   Finally, the Advertisement data is set and Advertisements are started.
+*/
+
+/* LISTING_START(ANCSSetup): ANCS Setup */
+void setup(void) {
+
+  Serial.begin(9600);
+  Serial.println("BTstack ANCS Client starting up...");
+
+  // startup BTstack and configure log_info/log_error
+  BTstack.setup();
+
+  sm_set_io_capabilities(IO_CAPABILITY_DISPLAY_ONLY);
+  sm_set_authentication_requirements(SM_AUTHREQ_BONDING);
+
+  // setup ANCS Client
+  ancs_client_init();
+  ancs_client_register_callback(&ancs_callback);
+
+  // enable advertisements
+  BTstack.setAdvData(sizeof(adv_data), adv_data);
+  BTstack.startAdvertising();
+}
+/* LISTING_END(ANCSSetup): ANCS Setup */
+
+void loop(void) {
+  BTstack.loop();
+}
+
+/*
+   @section ANCS Callback
+   @text In the ANCS Callback, connect and disconnect events are received.
+   For actual notifications, ancs_client_attribute_name_for_id allows to
+   look up the name. To get the notification body, e.g., the actual message,
+   the GATT Client needs to be used directly.
+*/
+
+
+/* LISTING_START(ANCSCallback): ANCS Callback */
+void ancs_callback(uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size) {
+  (void) packet_type;
+  (void) channel;
+  (void) size;
+  const char * attribute_name;
+  if (hci_event_packet_get_type(packet) != HCI_EVENT_ANCS_META) {
+    return;
+  }
+  switch (hci_event_ancs_meta_get_subevent_code(packet)) {
+    case ANCS_SUBEVENT_CLIENT_CONNECTED:
+      Serial.println("ANCS Client: Connected");
+      break;
+    case ANCS_SUBEVENT_CLIENT_DISCONNECTED:
+      Serial.println("ANCS Client: Disconnected");
+      break;
+    case ANCS_SUBEVENT_CLIENT_NOTIFICATION:
+      attribute_name = ancs_client_attribute_name_for_id(ancs_subevent_client_notification_get_attribute_id(packet));
+      if (!attribute_name) {
+        break;
+      }
+      Serial.print("Notification: ");
+      Serial.print(attribute_name);
+      Serial.print(" - ");
+      Serial.println(ancs_subevent_client_notification_get_text(packet));
+      break;
+    default:
+      break;
+  }
+}
+/* LISTING_END(ANCSCallback): ANCS Callback */
+