serial: uart_native_pty: IRQ support

Add support for the interrupt-driven API. Interrupts are
emulated using a polling thread.

Signed-off-by: Tim Pambor <tim.pambor@codewrights.de>

Author: tpambor

boards/native/native_sim/doc/index.rst

@@ -564,8 +564,7 @@ program ends, one could do:
 
    $ zephyr.exe --uart_attach_uart_cmd='ln -s %s /tmp/somename' ; rm /tmp/somename
 
-This driver supports poll mode or async mode with :kconfig:option:`CONFIG_UART_ASYNC_API`.
-Interrupt mode is not supported.
+This driver supports poll mode, interrupt mode and async mode.
 Neither runtime configuration or line control are supported.
 
 .. _native_tty_uart:

drivers/serial/Kconfig.native_pty

@@ -7,6 +7,7 @@ config UART_NATIVE_PTY
 	depends on (DT_HAS_ZEPHYR_NATIVE_PTY_UART_ENABLED || DT_HAS_ZEPHYR_NATIVE_POSIX_UART_ENABLED)
 	select SERIAL_HAS_DRIVER
 	select SERIAL_SUPPORT_ASYNC
+	select SERIAL_SUPPORT_INTERRUPT
 	help
 	  This enables a PTY based UART driver for the POSIX ARCH with up to 2 UARTs.
 	  For the first UART port, the driver can be configured