Make ‎TypedArray::update safe

[gterzian]

I think ‎TypedArray::update can be made safe, while containing an unsafe block calling Self::update_raw, that way we can remove these kind of unsafe blocks in Servo.

[Taym95]

How do you think we can do this @gterzian, from code I see unsafe code call is chained, update -> update_raw -> copy_nonoverlapping

[gterzian]

I think update should simply be safe externally, but internally have an unsafe block that calls update_raw(Otherwise there is no point in update_raw).