Select collapsible section text 'Click to expand' after inserting in plain text editor

What does this MR do and why?

Select collapsible section text 'Click to expand' after inserting in plain text editor

References

#595243 (closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Checkout this branch and run gdk locally
2. Go to any project's work item or MR page and open any single work item or MR
3. Go to the text editor at the bottom of the page
4. Click Switch to plain text editing button
5. Add collapsible section Clicking + button > Collapse section
6. Notice the text Click to expand is selected now. Now users can easily remove that default text and start typing.