The symlink solution taken in https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikibase/+/545382 appears to not work on Windows computers. The original task was T236206.
Possible solution (but sounds pretty terrible) https://stackoverflow.com/questions/5917249/git-symlinks-in-windows
Proposed solution, copy & paste with a CI check making sure that files are kept in sync.