test-copies: add 3 new files with their own content The new `p`, `q` and `r` file mirror the `a`, `b` and `h` but with different content for each files. This will be used to create "mirror" test case that involve actual merge happening. For now, we only add the file to keep patches small and easier to review. Differential Revision: https://phab.mercurial-scm.org/D10053