feat(wordpress): 1.2.2 tags simplepdf.com links with where they come from

[bendersej]

Background

SimplePDF's site now records where a visitor came from when a link carries ?ref=<source> (SimplePDF/simple-pdf#426). The plugin only tagged its pricing button, with ref=wordpress, and the WordPress.org listing used the same value, so plugin users and directory browsers could not be told apart.

Changes

• Every simplepdf.com link in the settings page (pricing, help center, how-to articles, guides) carries ref=wordpress_admin_settings, built in one helper
• The readme's simplepdf.com links (the WordPress.org listing) carry ref=wordpress_plugin_directory
• Version 1.2.2, with a changelog line saying the links carry nothing about the site or its visitors

Notes

• Merge after SimplePDF/simple-pdf#426 is deployed, so the new values are recorded from the first click (before that, the site ignores ref)
• Merging publishes 1.2.2 to WordPress.org and announces it (publish preview on this PR lists what ships)
• Checked in WordPress Playground: all 17 simplepdf.com links on the settings page carry the tag; the support mailto: link is untouched