Constellation panic caused by assertions

[asajeffrey]

We allow assert! and assert_eq! in the constellation. If these assertions fail, they will cause the constellation to crash, without providing any way for the user to submit a crash report. See, e.g. #11298.

If we decide not to allow such assertions, we should add a check to etc/ci/check_no_unwrap.sh (@aneeshusa).

[asajeffrey]

The easiest thing to do would be to replace assert by debug_assert, anyone running a debug build can probably work out how to submit a crash report from a raw panic. This would just hide a failed assert though, should we try to throw a mozbrowsererror event instead? (@paulrouget)

[nox]

We made constellation panic way less, and the general motto for constellation is to panic there. I think this can be closed now.