Port to Raspberry Pi Pico W core

Add support for the onboard WiFi chip on the Raspberry Pi Pico W
(RP2040 based ) board using the arduino-pico Arduino core at
https://github.com/earlephilhower/arduino-pico

The PicoW WiFi stack is a mashup of the ESP8266 and ESP32 cores, so
only minimal changes were required.  Defines a new NETWORK_TYPE for
the PicoW.

ESP8266 examples renames to ESP8266_PICO because they all work unmodified
(except for OTA which is handled differently on the Pico)

src/WebSockets.h

@@ -84,6 +84,15 @@
 #define GET_FREE_HEAP System.freeMemory()
 #define WEBSOCKETS_YIELD()
 #define WEBSOCKETS_YIELD_MORE()
+
+#elif defined(ARDUINO_ARCH_RP2040)
+
+#define WEBSOCKETS_MAX_DATA_SIZE (15 * 1024)
+#define WEBSOCKETS_USE_BIG_MEM
+#define GET_FREE_HEAP rp2040.getFreeHeap()
+#define WEBSOCKETS_YIELD() yield()
+#define WEBSOCKETS_YIELD_MORE() delay(1)
+
 #else
 
 // atmega328p has only 2KB ram!
@@ -104,6 +113,7 @@
 #define NETWORK_ENC28J60 (3)
 #define NETWORK_ESP32 (4)
 #define NETWORK_ESP32_ETH (5)
+#define NETWORK_RP2040 (6)
 
 // max size of the WS Message Header
 #define WEBSOCKETS_MAX_HEADER_SIZE (14)
@@ -118,6 +128,10 @@
 #elif defined(ESP32)
 #define WEBSOCKETS_NETWORK_TYPE NETWORK_ESP32
 //#define WEBSOCKETS_NETWORK_TYPE NETWORK_ESP32_ETH
+
+#elif defined(ARDUINO_ARCH_RP2040)
+#define WEBSOCKETS_NETWORK_TYPE NETWORK_RP2040
+
 #else
 #define WEBSOCKETS_NETWORK_TYPE NETWORK_W5100
 
@@ -201,6 +215,15 @@
 #define WEBSOCKETS_NETWORK_CLASS WiFiClient
 #define WEBSOCKETS_NETWORK_SERVER_CLASS WiFiServer
 
+#elif(WEBSOCKETS_NETWORK_TYPE == NETWORK_RP2040)
+
+#include <WiFi.h>
+#include <WiFiClientSecure.h>
+#define SSL_BARESSL
+#define WEBSOCKETS_NETWORK_CLASS WiFiClient
+#define WEBSOCKETS_NETWORK_SSL_CLASS WiFiClientSecure
+#define WEBSOCKETS_NETWORK_SERVER_CLASS WiFiServer
+
 #else
 #error "no network type selected!"
 #endif