tests: add criss cross merging tests whose behavior need to be fixed Merging two changesets can mark a file as removed post merge. However, in some cases, a user might not want to remove that file and they revert the removal back and commit the merge. All this works perfectly well. However, when we do criss-cross merges with such merge where user explicitly choose to revert the removal with one where another user choose the removal, we does not get any conflict. The intent here is conflicting and merge should result in conflicts. One user merged and want to keep the file while other user merged and want to remove the file. Merging those merges should result in conflicts. This patch adds test cases for these cases. Differential Revision: https://phab.mercurial-scm.org/D8939