drivers: uart: add support for serial ports on native posix

Add support for communication with serial ports on native POSIX platform
via UART driver API. Serial port driver supports polling API,
configuration of the serial ports used via devicetree and command line
options, and runtime configuration with `uart_configure`.
Multiple instances of the driver are supported.
Example use and configuration is also demonstrated in the
`samples/drivers/uart/native_tty` sample.

Closes: #56586

Signed-off-by: Marko Sagadin <marko.sagadin42@gmail.com>