XIAO RP2040, RP2040 SDK and APIs

A new release of Earle F. Philhower Arduino “core ” for RP2040 …

Release 2.6.0 - IDE 2.0 support and bugfixes

Add TARGET_RP2040 to build defines (#898)
Support IDE 2.0, detect UF2 volumes (#897)
Allow double-reset to jump to USB bootloader (#893)
Drive pin LOW after Tone(period) timeout (#887)
Fix Serial1/2 debug output mode in CoreMutex (#883)
Allow setCTS/RTS(UART_PIN_NOT_DEFINED) (#881)
Fix deadlock during attachInterrupt (#879)
Fix typo in HttpClient HTTPS example (#876)
Allow setting the WiFi region for PicoW (#875)

Guglielmo