Parser error recovery in `syn` for better IDE support with proc-macros

Tamschi:

Edit: I missed that the Warning variant emits when Tryd. Hm, not a huge fan of subtle side effects like that, to be honest, but that's personal preference.

"not a huge fan" is nice understatement Personally, I am violently opposed to that kind of thing.

As I put it in a hacking.md looking at try:

global state is inherently evil, hidden side-effects are inherently evil and usually rely on global state

But I did it anyway as I felt this was one of those rare cases where the ergonomic benefit vs the next best option made it viable. (My todolist has an entry to do the same again with tracing/logging depending on experience with diagnostics)