[A11y] [Issue 10] Focus order after "New messages" button is clicked

[compulim]

10 Severity 2 - Focus Management within chat

This is filed to #3136.

Background

At certain point in the conversation, “New messages” button appears. When the button is activated, focus moves to the first focusable element in the chat window instead of the new message.

Investigation notes

Explanations:

• When the "new message" button is clicked, the button is removed from the DOM tree. Since the focusing element is removed, the focus go back to the transcript
• On next TAB, it will focus to the next interactive elements on the transcript, which means the first button on the first interactive card

We need to investigate multiple solutions and I believe the solutions are same as the outcome of issue 8 (#3135).

Update 2020-05-11

Please see #3135 for updated investigation.

[Bug]

[compulim]

Fixed in #3150.