Update WixCop to migrate v3 source code to v4.0

[wixbot]

There are many changes to the WiX schema in WiX v4.0. WixCop needs to be updated.

Originally opened by firegiantco

[wixbot]

Should be addressed by #60

Originally posted by firegiantco

[rseanhall]

@firegiantco Is this completed or was it intended to stay open until we ship v4.0?

[barnson]

Modulo bugs, it's "done" -- until/unless we make other changes to the v4 schema. Probably fine to track with a work item to point to. (Not usually a fan but I accept it's handy to have a work item to point to in release notes.)

[robmen]

The 'wix convert' work is complete for now. Additional needs will use specific conversion issues.