backports: UART pin attachment from 3.0.0 to 2.0.15

* feat(uart): backports UART pin attachment from 3.0.0 to 2.0.15
* Fix (uart): Fixes additional Serial HardwareSerial errors for 2.0.14
* Update esp32-hal-uart.c
* Update HardwareSerial.h
* Apply suggestions from code review
* Fixes UartAvailableForWrite
* Fixes  (set RX/TX buffer size)

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Co-authored-by: Rodrigo Garcia <[email protected]>

Author: Jason2866