revset: rename diff(pattern) to diffcontains(pattern) Suggested by Augie, and I think it's better name.

pyoxidizer: update to PyOxidizer 0.9 We were previously using a Git commit from a few days before the 0.8 release. This commit upgrades us to the just-released 0.9 release. This required some Starlark changes due to backwards incompatible changes. Differential Revision: https://phab.mercurial-scm.org/D9228