Also const-ify and refactor a few things in BytecodeAnalysis.

Change-Id: Ibd261bb67d8c035b1f818e9114d09db08737000d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1587384
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61088}