tests: Convert all machine.UART tests to use target_wiring.

All the existing `machine.UART` tests in extmod and extmod_hardware are
converted to use the new `target_wiring` scheme, which removes a lot of
duplicated board-specific settings.

All the existing boards that were supported by these UART tests now have
their own `target_wiring` file.  Some configurations are board specific (eg
NUCLEO_WB55) and others are port specific.

Signed-off-by: Damien George <damien@micropython.org>

tests/target_wiring/esp32.py

@@ -0,0 +1,7 @@
+# Target wiring for general esp32 board.
+#
+# Connect:
+# - GPIO4 to GPIO5
+
+uart_loopback_args = (1,)
+uart_loopback_kwargs = {"tx": 4, "rx": 5}