templater: swap `\` with `/` to allow the resource logic to kicks in Without this change our wrapper to the resource logic will fails to details the nesting and try to pass `directory/file` entry to the resource module, leading to a crash. Ideally, we should track down all caller passing `\` instead of `/`, but that is far more intrusive and we would like to have a working pyoxidized version working for 5.9 It will be easy to add a warning to the above code to track down "bad" caller during the 6.0 cycle. This reduce the number of failing test with pyoxidizer from 52 to 23 Differential Revision: https://phab.mercurial-scm.org/D11281