[NTP XDTR] Move blocklist/pref logic to util

Move blocklist to shared location so Quests and Tab Resumption modules
can share the same blocklist.

Bug: 328232995
Change-Id: If6bcb18bd364ae47ece0386c62e4c46e15edaba2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5402057


Reviewed-by: Roman Arora <romanarora@chromium.org>
Commit-Queue: Marlon Facey <mfacey@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1280271}