copies-rust: add methods to build and update CopySource Having explicit method with clear semantic help to clarify the code and prepare an update to the underlying documentation without too much disruption. Differential Revision: https://phab.mercurial-scm.org/D9643

copies-rust: fix reverted argument when merging tiny minor or major The argument where not passed in the right other. This is not caught by the test (yet) because it is a sub case of a special case. Am I adding this to my list of things to test. Using test directly in Rust would be appropriate here. However we don't have the ability to test this code that way yet, and I am focussing on other part of that work right now. Differential Revision: https://phab.mercurial-scm.org/D9657