Accessibility: Administration: Give the link to meetup organizer handbook in...

Accessibility: Administration: Give the link to meetup organizer handbook in the WordPress Events and News dashboard widget a more meaningful label.

This ensures that the link still makes sense when read out of context by assistive technologies.

Additionally, underline the link per the accessibility coding standards.

Props samful, afercia, williampatton, audrasjb.
Fixes #50338.
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git-svn-id: https://core.svn.wordpress.org/trunk@47915 1a063a9b-81f0-0310-95a4-ce76da25c4cd