[bedrock] Update Browser to use the CLIENT_OWNS_WIDGET ownership scheme

This CL updates Browser instances to leverage the views::Widget
CLIENT_OWNS_WIDGET ownership scheme, transitioning away from the
existing implementation using NATIVE_WIDGET_OWNS_WIDGET.

This aligns with current best practices and simplifies the exiting
Browser ownership structure.

This CL makes the following changes:

  - Browser owns a unique_ptr<BrowserWindow>
     - For Views impls BrowserView is owned by the Views hierarchy
       of its BrowserFrame / views::Widget, and is destroyed when
       BrowserFrame is destroyed. A custom deleter has been
       introduced to give BrowserView the ability to correctly
       sequence this teardown while maintaining existing BrowserView
       destruction expectations wrt its host Widget

  - Instantiates the BrowseManagerService, added in the upstream
    crbug.com/c/6904683
      - It is not possible to simply vend clients unique_ptr<Browser>
        instances in Browser::Create() as almost all existing clients
        expect to receive self-owned Browser raw ptrs

  - BrowserFrame::OnNativeWidgetDestroyed() is added to maintain
    existing expectations that when the associated NativeWidget is
    destroyed, the Browser instance is also synchronously destroyed.
      - There are exiting clients / tests that will call
        BrowserFrame::CloseNow() and expect immediate cleanup

  - Fixes existing unit tests to align with the new ownership scheme

Include-Ci-Only-Tests: true
Bug: 413168662
Change-Id: I209f2a739ff0d4731528dd7d6bc810fd618b8656
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6883931
Commit-Queue: Tom Lukaszewicz <tluk@chromium.org>
Reviewed-by: Dana Fried <dfried@chromium.org>
Reviewed-by: Keren Zhu <kerenzhu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1510761}