When a plugin states it requires a specific minimum PHP version (as defined in the `requires_php` field included in the plugin update API response), a user should not be allowed to update that plugin when the server does not satisfy the minimum PHP version.
When this scenario is encountered, the update buttons and links are disabled and links to educational resources about PHP are displayed to the user with a notice.
Props afragen, schlessera, desrosj.
Fixes#43987.
git-svn-id: https://develop.svn.wordpress.org/trunk@44937 602fd350-edb4-49c9-b593-d223f7449a82