Rather than walking SharedFunctionInfos recursively via bytecode
constant pools to ensure they have source positions, walk the script's
shared function info list.

Bug: chromium:1011762
Change-Id: I19ab0f3355dc8169f7a0170b4198075bd3823c04
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2084816
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66571}