Toolbar: In Comments link, replace title attribute containing the number of...

Toolbar: In Comments link, replace title attribute containing the number of pending comments with a screen reader text.

Props slushman, rachelbaker.
Fixes #34895.
Built from https://develop.svn.wordpress.org/trunk@36093


git-svn-id: https://core.svn.wordpress.org/trunk@36058 1a063a9b-81f0-0310-95a4-ce76da25c4cd