Handle panicking like rustc CTFE does
Instead of using `core::fmt::format` to format panic messages, which may in turn panic too and cause recursive panics and other messy things, redirect `panic_fmt` to `const_panic_fmt` like CTFE, which in turn goes to `panic_display` and does the things normally. See the tests for the full call stack.
The tests don't work yet, I probably missed something in minicore.
fixes#16907 in my local testing, I also need to add a test for it
6f6b03f9de