scmutil: introduce filterrequirements() to split reqs into wc and store ones In upcoming patches where we try to implement requirements in store, we will need a mechanism to split all requirements on some basis and decide which one goes to `.hg/requires` and which one goes to `.hg/store/requires`. This patch introduce a separate function for that. Filtering logic for now is put under an `if False:`. In upcoming patches it will be removed. Differential Revision: https://phab.mercurial-scm.org/D8913