Add an `h1` heading with the existing `login_header()` text string on each view of the login screen. Mark the existing `h1`, used to wrap the WordPress logo, with `role="presentation"`, to remove it from the headings hierarchy.
Props roytanck, joedolson, ryokuhi, sabernhardt, pamprn, nagpai, mukesh27.
Fixes#51786.
Built from https://develop.svn.wordpress.org/trunk@59138
git-svn-id: http://core.svn.wordpress.org/trunk@58534 1a063a9b-81f0-0310-95a4-ce76da25c4cd
