This is a strictly code moving change. We move the diffing algorithm
out of liveedit.cc into its own file.

We want to replace the current diffing algorithm and to stay safe we
will ship old and new algorithm side-by-side for a release for easy
revertability. Given that liveedit.cc is already large enough we
extract the diffing algo into a separate file.

R=kimanh@chromium.org

Bug: chromium:1205288
Change-Id: If5ebb6c2dff2f00387c9e2ab87e4bb61d1f1484a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3802687Reviewed-by: Kim-Anh Tran <kimanh@chromium.org>
Commit-Queue: Simon Zünd <szuend@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82124}