Make interrupt module more standard.

- Move typelevel interrupts to a special-purpose mod: `embassy_xx::interrupt::typelevel`.
- Reexport the PAC interrupt enum in `embassy_xx::interrupt`.

This has a few advantages:
- The `embassy_xx::interrupt` module is now more "standard".
  - It works with `cortex-m` functions for manipulating interrupts, for example.
  - It works with RTIC.
- the interrupt enum allows holding value that can be "any interrupt at runtime", this can't be done with typelevel irqs.
- When "const-generics on enums" is stable, we can remove the typelevel interrupts without disruptive changes to `embassy_xx::interrupt`.

embassy-stm32/src/exti.rs

@@ -354,13 +354,13 @@ impl_exti!(EXTI15, 15);
 
 macro_rules! enable_irq {
     ($e:ident) => {
-        crate::interrupt::$e::enable();
+        crate::interrupt::typelevel::$e::enable();
     };
 }
 
 /// safety: must be called only once
 pub(crate) unsafe fn init() {
-    use crate::interrupt::Interrupt;
+    use crate::interrupt::typelevel::Interrupt;
 
     foreach_exti_irq!(enable_irq);