[Merge to M131] preload: Introduce kMouseHoverOrMouseDownOnNewTabPage

This CL introduce kMouseHoverOrMouseDownOnNewTabPage to replace
kMouseHoverOnNewTabPage and kPointerDownOnNewTabPage, since the
current mechanism used for holdback group experiment doesn't
support multiple PreloadingPredictors. See
https://docs.google.com/document/d/18RAbIcbL53rJZY6FH4ONQWcITKWQspLMK6TCJsMYXSY/edit?usp=sharing
for more details.

(cherry picked from commit 8ffdfbc4)

Bug: 376421273
Change-Id: I30c60c9148fa1a06a7db2ae6f57f487ea87f8518
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5981651


Reviewed-by: Lingqi Chi <lingqi@chromium.org>
Reviewed-by: Paul Adedeji <pauladedeji@google.com>
Commit-Queue: Huanpo Lin <robertlin@chromium.org>
Cr-Original-Commit-Position: refs/heads/main@{#1376293}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5981416
Cr-Commit-Position: refs/branch-heads/6778@{#1675}
Cr-Branched-From: b21671ca-refs/heads/main@{#1368529}