This removes level-triggered interrupts.
While working on https://github.com/tinygo-org/tinygo/pull/3170, I found
these level triggered interrupt constants. Apart from them being
inconsistent with each other (PinLowLevel vs PinLevelLow) I don't think
they are actually used anywhere. In addition, I removed the
PinNoInterrupt constant on the esp32c3. This makes the esp32c3 pass the
tests in #3170.
I looked into level-triggered interrupts and I really couldn't find a
good justification for them:
- They were added to the esp32c3 and the rp2040 together with other
pin interrupt types, meaning they were probably just added because
the chip supports the feature and not because they were actually
needed.
- Level interrupts aren't supported in TinyGo for any other chip, and
I haven't seen anybody ask for this feature.
- They aren't supported in the nrf series chips _at all_, and with a
quick search I found only very little demand for them in general.
- I tried to see whether there is any good use case for them, but I
couldn't really find one (where an edge triggered interrupt wouldn't
work just as well). If there is one where level triggered interrupts
are a real advantage over edge triggered interrupts, please let me
know.
Of course, we shouldn't remove a feature lightly. But in this case, I
can't think of an advantage of having this feature. I can think of
downsides: more maintenance and having to specify their behavior in the
machine package documentation.
In general, I would like to keep the machine package clean and only
support things that have a proven use case.
