[Settings containment] Add background styling to BaseSiteSettings

This change applies the settings containment background styling to
BaseSiteSettingsFragment and its subclasses.

The preferenceScreen can be null in onCreateRecyclerView in cases
such as All Site settings where preferences are created
asynchronously to avoid jank. Creating the SettingsStylingController
in updateBackgrounds ensures the preferenceScreen is always ready.

Before: https://screenshot.googleplex.com/r3AC953iw59Gb9Q.png
After: http://screencast/cast/NDgyMzk1NDQ2NzMyMzkwNHxjN2UwMjE4Zi1mYw

Bug: 433576895, 438273935
Change-Id: I46b8e70636ebf1caff426d6585cd724859c6043c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6854437
Reviewed-by: Wenyu Fu <wenyufu@chromium.org>
Commit-Queue: Gazal Agarwal <agazal@google.com>
Cr-Commit-Position: refs/heads/main@{#1502925}