1445260 - add release-mode bounds checking to Vector::operator[] et al and associated iterators

Status: NEW

(Core :: MFBT, enhancement)

Description

[Nathan Froyd [:froydnj]]

We did this for nsTArray in bug 1159244 (and others) and it caught a number of errors.  Rust has this by default and we can too.

Note that there probably *does* need to be a fallback to do unchecked accesses, for code that absolutely, positively, always does in-bounds accesses and simply cannot afford the extra checks.  But said fallback should be somewhat loud and obnoxious to make it obvious what's going on and to discourage casual use.

It may be simpler to just add release-mode bounds checking for operator[] and then extend the release-mode bounds checking to other functions and iterators in separate bugs.