WIP: release hardening, sites_linkit extraction, sites_example examples +...

Pascal Crottrequested to merge
issue/sites-3607366:3607366-1.0.0-prep-per-bundle into 1.x

WIP: release hardening, sites_linkit extraction, sites_example examples + sites_test fixtures, site cache tags, O(matches) resolution (scaling phase 1), PHPStan L4, tests

Closes #3607366

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