getrenamedfn: get copy data from context object if configured
The function returned from getrenamedfn() calls
filelog.renamed(). That won't work when storing copy metadata in the
I've just switched to a simple implementation here. We may or may not
need to optimize it later, possibly by optimizing the callers.
No more tests fail with "--extra-config-opt
experimental.copies.read-from=compatibility)" than they did before
Differential Revision: https://phab.mercurial-scm.org/D6162