Split new page actions code into a module

This CL shouldn't change behaviour.

Page actions are being refactored such that the responsibility of
controlling a page action will fall on the feature, rather than having
page actions control all features (i.e. 1 depends on N vs N depends on 1). Therefore, splitting out page actions code into its own module will make the migration easier as features introduce this dependency.

Note 1: The legacy page actions code (e.g. `page_action_icon_view.h`) is not included in this new BUILD target because these will ultimately be removed at the end of the migration and untangling them now is non-trivial effort.

Note 2: Page actions currently have a dependency on "c/b/ui/views/location_bar", which is part of "c/b/ui:ui", which is causing a circular dependency. Location bar should also be modularized, but this is non-trivial and out-of-scope of the page actions refactoring.

Bug: 376285151
Change-Id: I8580620336b1db587a731584f8700673c95aacc1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6049520
Reviewed-by: Dana Fried <dfried@chromium.org>
Commit-Queue: Kaan Alsan <alsan@chromium.org>
Reviewed-by: Caroline Rising <corising@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1391126}