flagprocessors: add a `sidedata` parameters to _processflagswrite
To read sidedata using flagprocessors, we need flag processors to store them. So
we pass this information to the flag processing layer.
Differential Revision: https://phab.mercurial-scm.org/D6815
revlog: add a `sidedata` parameters to addrevision
If we want to eventually store sidedata we need to be able to pass them along.
Differential Revision: https://phab.mercurial-scm.org/D6814
flagprocessors: have the read transform function return side data (API)
This makes it possible for flag processors to -read- flag data.
Differential Revision: https://phab.mercurial-scm.org/D6813