Opt into fully transitive copies under a change wave

[rainersigwald]

Before change waves existed, we didn't have a way to opt into reasonable behavior in #4865, so we left the default as it was. But that's confusing, broken, and hard to discover that you need to opt into one of the reasonable states.

We should opt into MSBuildCopyContentTransitively=true under a change wave (16.10?).

[rainersigwald]

I reactivated #1054 so calling this a dupe.

[rainersigwald]

Duplicate of #1054.