WiFiServer - operator bool() and method end()

[JAndrassy]

I did a research how different Arduino networking libraries implement the Arduino networking API.
https://github.com/JAndrassy/Arduino-Networking-API/blob/main/ArduinoNetAPILibs.md#server-class

For most libraries it is simpler to implement operator bool() than the method status() with its return value constants. So this PR adds bool operator for WiFiServer in the ESP8266Wifi library.

In the research I find out that end() is the most popular name for the function to stop the server and Arduino now used it too in the new WiFiS3 library.

[earlephilhower]

That's a darn odd failure in CI. I have no idea what's going on there w/host builds and don't think it's related to this at all.

That said, maybe add those methods to wired Ethernet too? https://github.com/esp8266/Arduino/blob/master/cores/esp8266/LwipIntfDev.h My bad, not related.

Would you also like to do the same PR for https://github.com/earlephilhower/arduino-pico ? I could add the add'l functions, but since you've identified the problem I don't want to steal your thunder. We now have wired and WiFi support there, stolen borrowed from here. 😆

[JAndrassy]

@earlephilhower I already do to many PR and write issues as a result of the research. Most of the [PR] and [issue] links in the document are my PR and issues. Please do the changes in the Pico core.

btw I didn't include the libraries from pico core in the research since the WiFi is only for Pico W and the libraries for wired Ethernet were not ready when I started :-)

[mcspr]

Same q as above, don't we want this in Server base?
Otherwise, same thing must be copied to Lwip server implementations