* WiFiServer - 'rename' available() to accept()
* use server.accept() instead of available()
* WiFiServer.accept() and ArduinoWiFiServer class doc update
* Add Print::availableForWrite method
Adds an availableForWrite() method to the Print class, matching current
ArduinoCore-API commit 398e70f188e2b861c10d9ffe5e2bfcb6a4a4f489 .
Hook availableForWrite into the SDFS filesystem (other FSes don't have
this capability built-in).
Fixes#7650
* WiFiClient::availableForWrite proto matching Print
* Fix Netdump signedness warning
* Clean up Serial availableForWrite
This is evidently a breaking change due to the type difference.
Arduino's `availableForWrite` returns an `int`, while the
(multiply-implemented, non-virtual) core `availableForWrite` returned
`size_t`.
