We often use ResultBase or VoidResult to store or pass wasm errors
(errors with locations). This CL extracts a WasmError class which can
store an error (can also be empty), and Result<T> which stores an error
or a T (exactly one of them).

R=titzer@chromium.org

Bug: v8:8689
Change-Id: I3f5203559984a0ae8757e0130a9184957fa28df5
Reviewed-on: https://chromium-review.googlesource.com/c/1409365
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58827}