Panic when DefaultHandler gets invoked

[bjoernQ]

The DefaultHandler can never do something much more useful than panicking

Fixes #1001

Easy check: Use the gpio_interrupt.rs example and remove the interrupt handler. Pressing the boot button will now panic instead of silently do nothing anymore

[MabezDev]

What's the difference between EspDefaultHandler and DefaultHandler? Shouldn't we get rid of DefaultHandler and push everything through EspDefaultHandler or am I missing something?

[bjoernQ]

Yeah EspDefaultHandler is what I wanted to use in the first place but it didn't work. Now it does

[MabezDev]

I think I got it wrong, I think DefaultHandler is for CPU level interrupts i.e 0-31 on either RISCV or Xtensa, and EspDefaultHandler is the default handler for when a #[interrupt] handler is missing. So I think we need both, but I have no idea why DefaultHandler was Xtensa only before 🤔.

[bjoernQ]

It's even a bit more complicated because DefaultHandler is used in the device.x in PACs - I don't know if we can change that.
Now with this we would get something very ugly for unhandled CPU level interrupts... but at least not nothing

[bjoernQ]

But I think we could only end up there from a CPU level interrupt on Xtensa for something > level 3 ... which would be a problem on its own. For RISC-V we should always end up in start_trap_rust_hal

So maybe it's not that bad

[MabezDev]

I actually just used this PR to find out which interrupt was putting me in the DefaultHandler :D. LGTM! Just needs a rebase I think :)