Enable kBoostRenderProcessForLoading feature on non-Android

This change enables the kBoostRenderProcessForLoading feature by default
on all platforms except Android. This feature aims to improve page load
speed by boosting the renderer process priority during the loading
phase.

Result (google internal):
https://docs.google.com/document/d/1fYwyjNsWRc5rUdC96V4fPhGRUOERjmaQf1qA9JTh7sM/edit?resourcekey=0-bHeiHfDisxxMR6Vs4TwI9A&tab=t.0#heading=h.dwblcms3emv0

Enabled-by-default-reason: launching
Bug: 351953350
Change-Id: I4b9f336f8328746a1b66017facc7463b98df3a7b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6927872
Reviewed-by: Rakina Zata Amni <rakina@chromium.org>
Reviewed-by: Yoshisato Yanagisawa <yyanagisawa@chromium.org>
Commit-Queue: Minoru Chikamune <chikamune@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1513473}