Add UninstallMsiPackage/@ProductCode to let Burn uninstall packages

[wixbot]

It's sometimes necessary to uninstall packages before upgrading them, when major upgrades can't do something correctly (e.g., cross-scope upgrades or file downgrades). You can fake a package to have Burn handle this but making it idiomatic would simplify the work.

Originally opened by barnson

[wixbot]

I think this would also be helpful for packages that install assemblies to the GAC. IIRC, major upgrades don't work very well unless you get the scheduling just right (and I think we still ran into problems so we just forced users to uninstall first).

Originally posted by jack hennessey

[wixbot]

Needs a WIP.

AssignedTo set to bobarnson