[2.0.x] Enable hardware serial ports on LPC1768 (#8004)
* Enable hardware serial ports on LPC1768
* Fix compilation errors with other HALs
* FIx order of includes in LPC1768 HAL main.cpp
* Add support for RX_BUFFER_SIZE and TX_BUFFER_SIZE options in Configuration_adv.h
* Fix mistake in gitignore file and add in missing core files.
The missing leading slash on "lib" meant all folders names lib in the directory tree are ignored, rather than just the top level PlatformIO lib folder
* Add LiquidCrystal Library and associated headers modified to compile.