Branch for MLIR environment

[sogartar]

@ChrisCummins, is it possible to have a branch for the MLIR env? It looks like that its merging will take a while due to its size and the step(...) breaking changes. We want to collaborate on it with other developers.
The branch can be called mlir. For the time being I would like for me and @KyleHerndon to have push access to it. Later others will join.

[ChrisCummins]

In general I try not to have long-running staging branches but I think in this case it makes total sense.

Feel free to work on mlir however you want and just add me to PRs when you have things you want to merge into development. It would be worth periodically syncing with the development branch as there will be the occasional breaking change that you might find useful (e.g. #591).

I've given you and Kyle push permission on this repo, let me know if there are any problems.

Cheers,
Chris