This is the same functionality provided by `npm test:size` in Minerva
and Vector skins, but as a structure test. Any extension/skin that
provides bundlesize.config.json containing an array of expected gzipped
sizes and module names will be processed by this test.
See also WikimediaMaintenance's blameStartupRegistry.php for similar
code.
Bug: T255149
Change-Id: Ieb7591f3c0ac843677a2a61b4ad47f920fc2ca2d
