Print def_id on EarlyBoundRegion debug
It's not the first time that I can't make sense out of the default debug print on `EarlyBoundRegion`. As I was working on #112682 I needed this.
I was doing some git archeology and found that we used to print everything dfbc9608ce/src/librustc/util/ppaux.rs (L425-L430)
but we lost the ability in some refactor midway.