When it is difficult to navigate a function, it is overdue to split
it up :D
Also, no need to test for feature `gpio_ll_irq` in `test_irq()` *and*
before calling `test_irq()`.
The documentation on the state `GPIO_DISCONNECT` was a bit vague. The
API doc said it should disconnect the GPIO from all peripherals, the
test also tested them for being electrically disconnected.
The documentation in both the test and the API is extended to point out
that a GPIO indeed SHOULD be in high impedance state, but that user
MUST NOT expect that this requested is honored by every implementation
and for every GPIO pin.
In the test it is also pointed out that failing the test for a GPIO
in the `GPIO_DISCONNECT` state being electrically disconnected is for
some pins expected, and that the test should be just run again with
different GPIOs. The test intentionally tests for a feature not provided
by every GPIO pin rather than warning on a failure: The effort to just
flash and run the test again with different GPIOs is relatively low, but
it does confirm correct behavior of the API.
When using level triggered IRQs, a new IRQ flag may already have been
set while the IRQ callback is executed. Hence, we cannot just toggle
the output, but rather should drive it low/high for a level trigger on
high/low.
Also test `gpio_ll_query_conf()` for the disconnected state as well.
Printing the newline after the state was printed is not optional.
This also moves the call to `gpio_ll_print_conf()` and `puts("")` to
a static function to safe enough ROM so that this still can be flashed
on `nucleo-l011k4`.
