This removes the {error} and {verror} methods of {ResultBase} and
introduces a named constructor {Error} instead. This allows to
construct an error result in a single expression, and moves {Result}
closer to a container that is initialized once and is immutable
afterwards (just the {MoveErrorFrom} method is still violating this
pattern).

R=titzer@chromium.org

Bug: v8:8238
Change-Id: Iec16c8c6d66300ee82a48e8a9e941c72ae26e202
Reviewed-on: https://chromium-review.googlesource.com/c/1293370
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56857}