This is taken from the abandoned error stacks proposal, which
already serves as the source of truth for the setter. It only requires
the this value to be an object - if it's not an Error object, the getter
returns undefined.
I have not compared this behavior to the non-standard implementations of
the stack property in other engines, but presumably the spec authors
already did that work.
This change gets the Sentry browser SDK working to a point where it can
actually send uncaught exceptions via the API :^)
Some of this stuff is already tested properly in the name and message
prototype tests, so let's focus on covering all error types here as well
instead.
Otherwise these will get their name/default message from the Error
prototype, and as a result would always just say "Error" in error
messages, not the specific type.
Something I missed in da177c6, now with tests. :^)
