In the previous refactoring --filter was accidentally filtering out
paths that matched <regexp>. This CL restores the original behavior
where only the matching paths are kept.

Bug: v8:12821, v8:11113
Change-Id: I7e7d7b793107fbf9b4944b1674874150803f4bb4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3623539
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80426}