F6 should allow navigating to RHS even if a thread isn't open

Description

F6 loop should include search results/any content in the RHS in the same looping slot as the RHS comment threads are currently. If the RHS is not open, just skip that loop slot (as is implemented now).

Focus behaves the same as posts in the center pane (so arrow keys can be used to navigate search results/recent mentions/flagged posts/pinned posts).

Focus should start on the top post in the search results/recent mentions/flagged posts/pinned posts list when F6ed into this area. The entire post should be focused similar to F6ing in the center pane. When focused, screen reader should read the header, eg "Direct Message (with Stu Doherty)", then read the post in the same manner as it does in the center pane.

QA Test Steps

1. Open Mattermost on Windows.
2. Open the Recent Mentions window
3. Press F6 (Ctrl or Cmd+F6 if in a browser) three times.
4. The first post in Recent Mentions should be highlighted.
5. Press Up and Down arrows.
6. You should be able to use them to navigate through the posts on the RHS.
7. Open JAWS, and navigate through the posts.
8. You should hear JAWS read the posts out in the same fashion as the center channel.

Reporter

None

Status

Mana

4

Assignee

Devin Binnie

QA Assignee

Lindy Isherwood

Reporter

Eric Sethna

Mattermost Team

Apps

Sprint

None

QA Testing Areas

RHS

GitHub Issue

None

Components

None
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