dirmgr: Expopse DirMgrStore

Ian Jacksonrequested to merge
Diziet/arti:store3 into main

This is an opaque type, and all you can do with it is make one, and pass it to the DirMgr and BridgeDescMgr constructors.

This is needed for #631 (closed). The solution is not the one mentioned in #631 (comment 2853665) and is in fact simpler than that.

The branch is on top of !845 (merged) which I think is unblocked, but has not yet been merged.

Merge request reports