Press This accessibility improvements

[afercia]

Proposed patch addresses following issues, some of them marked as "errors" by WAVE evaluation tool:

Errors:

• 2 X Missing form label (url-scan and wp-editor-area, won't touch the latter)
• 1 X Empty form label (search categories)
• 1 X Empty heading (won't touch this, there's ongoing discussion on this h2)
• 1 X Empty button (add-cat-toggle button-subtle)

Additionally:

• added some screen-reader-text and aria-hidden attributes
• added "aria-expanded" on some buttons
• focus handling improvements
• added missing target id for aria-controls="pressthis-code-wrap" in /wp-admin/tools.php
• changed tagcloud-link into a button

[stephdau]

Patch is looking good and working well in my test of it.

[azaozz]

In 31566:

PressThis: accessibility enhancements:

• Add missing form labels.
• Add some screen-reader-text and aria-hidden attributes.
• Focus handling improvements.
• Change tagcloud-link into a button.
• Add missing ID attribute in tools.php.

Props afercia. Fixes #31449.