Adds new tests for localized sites as well as the dashboard.
Also amends Server-Timing output to measure memory usage in all scenarios.
Props swissspidy, joemcgill, flixos90, mukesh27, mamaduka.
See #59656.
Fixes#59815.
git-svn-id: https://develop.svn.wordpress.org/trunk@57083 602fd350-edb4-49c9-b593-d223f7449a82
