Add aria-labels and title attributes to icon hyperlinks in the header toolbar

[claytoncollie]

Description of the Change

Issue #2286

Alternate Designs

This was the least intrusive option. The second option would be tooltips on each icon which would require additional javascript. The third option would be to add a text label just below the icon which probably involves some sort of design change and sign-off.

Benefits

1. Screen readers will be able to identify the links
2. New users will understand the icon's function before selecting it

Verification Process

To verify, I went to the wp-admin dashboard for the plugin and hovered over each icon to see the title attribute.

Also ran composer run lint-fix in my editor to make sure my code formatting was correct.

Checklist:

• [X ] I have read the CONTRIBUTING document.
• [ X] My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Changelog Entry

Add title attributes and aria-labels to each icon hyperlink in the header toolbar