Replaced all occurrences of AstId with BytecodeOffset

Change-Id: I5bee2d35ccd6e404748ba352e35f5982a7a9b392
Reviewed-on: https://chromium-review.googlesource.com/561007
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46472}