Fixes LookupNameOfBytecodeHandler so it actually returns non-nullptr
values with embedded builtins enabled. Also now correctly handles wide
and extra-wide bytecodes and always works regardless of whether
ENABLE_DISASSEMBLER is set.

Bug: v8:9215
Change-Id: I787134f2145d02daaf5b50ecb6c174dfc129a4fe
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1635890Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61929}