Similar to T303102: Normalise PHP namespaces used in Vector
Most of the code is in MediaWiki\Minerva\. This also should probably be considered non standard (and inconsistent too) based on https://www.mediawiki.org/wiki/Best_practices_for_extensions#File_structure; however Minerva is sufficiently unique that this is allowed.
Tests are in Tests\MediaWiki\Minerva and MediaWiki\Skins\MinervaNeue\Tests\.