Accessibility: Simplify the Site Health score indicator.

The Site Health score indicator isn't exactly a "progress bar" and shouldn't use ARIA roles and properties related to progress bars. Also, some browser / screen reader combinations don't announce the score properly.
- removes any ARIA
- adds a screen-reader-text "Current health score:"
- adds `role="img" aria-hidden="true" focusable="false"` to the SVG
- reduces CSS specificity simplifying unnecessary overqualified selectors
- fixes the syntax for ::after and ::before (double colon)

Fixes #46621.

Built from https://develop.svn.wordpress.org/trunk@45041


git-svn-id: http://core.svn.wordpress.org/trunk@44850 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.2-alpha-45040';
+$wp_version = '5.2-alpha-45041';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.