Focus handling when sidebar panel webview is opened and closed

[simonhong]

When sidebar panel opens, give focus to sidebar panel.
When sidebar panel closes, clear focus. Browser window's root view will get focused.

STR 1 - panel open

1. Open sidebar bookmarks panel

• Actual result - bookmarks panel don't have focus
• Expected result - bookmarks panel has focus
  After opening bookmarks panel, first tab gives focus to first element in the panel

STR 2 - panel close

1. Open sidebar bookmarks panel
2. Click any area in sidebar bookmarks panel to get focus
3. Close sidebar bookmarks panel

• Actual result - web page in active tab gets focused always.
  If active tab is github.com, we can see below Skip to content element after panel is closed.
  
• Expected result - Focus is cleared

[kjozwiak]

Requires 1.37.90 or higher for QA verification's via 1.37.x.

[stephendonner]

Verified PASSED using

Brave	1.37.90 Chromium: 99.0.4844.51 (Official Build) beta (x86_64)
Revision	d537ec02474b5afe23684e7963d538896c63ac77-refs/branch-heads/4844@{#875}
OS	macOS Version 12.3 (Build 21E230)

Case One: panel open

1. installed 1.37.90
2. launched Brave
3. clicked on the Bookmarks icon in the Sidebar
4. to check focus, pressed tab

Confirmed tab cycled through UI elements in their index

example	example

Case Two: panel close

1. installed 1.37.90
2. launched Brave
3. clicked on the Bookmarks icon in the Sidebar
4. clicked to expand a folder with a bookmark
5. pressed tab to select the bookmark
6. clicked on the Bookmarks icon in the Sidebar to close the panel

Confirmed NO Skip to content (from test plan) present on panel close. (I was able to trigger that accessibility navigation hint normally via tab which is expected in that context.)

example	example

[btlechowski]

Verification passed on

Brave	1.37.95 Chromium: 99.0.4844.74 (Official Build) beta (64-bit)
Revision	fee9a47e86e981802390cb0d41c5ed7ea93c4f6f-refs/branch-heads/4844@{#1060}
OS	Ubuntu 18.04 LTS

Verified test plan from the description

panel open

Verified bookmarks panel has focus

panel close

Verified focus is cleared

[MadhaviSeelam]

Verified 'Passed' using

  Brave |	1.37.98 Chromium: 99.0.4844.74 (Official Build) beta (64-bit) 
  --|--
  Revision |	fee9a47e86e981802390cb0d41c5ed7ea93c4f6f-refs/branch-heads/4844@{#1060}
  OS |	Windows 11 Version 21H2 (Build 22000.556)

Case One: panel open

• installed 1.37.98
• launched Brave
• clicked on the Bookmarks icon in the Sidebar
• to check focus, pressed tab to focus on the first element in the panel
• Confirmed tab cycled through UI elements in their index

panel open

Case Two: panel close

• installed 1.37.98
• launched Brave
• clicked on the Bookmarks icon in the Sidebar
• clicked to expand a folder with a bookmark
• pressed tab to get focus
• Clicked on the Bookmarks icon in the Sidebar to close the panel
• Confirmed NO Skip to content (from test plan) present on panel close.

panel close