Replace usage of g_settings_new() with ui::GSettingsNew()

* Move //ui/base/glib to a separate source_set since to avoid a circular
  dependency since //net needs to depend on it.
  - Add build dependencies on //ui/base/glib
* Remove usages of g_settings_new()

R=thestig

Bug: None
Change-Id: I872e1c6a9da4ff10d2ee43009809d9ec5ac1edae
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6419125
Reviewed-by: Aaron Leventhal <aleventhal@chromium.org>
Commit-Queue: Zonghan Xu <xzonghan@chromium.org>
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Reviewed-by: Lambros Lambrou <lambroslambrou@chromium.org>
Commit-Queue: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Auto-Submit: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Zonghan Xu <xzonghan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1443631}