BeforeBuild should be available in outer builds

### Steps to reproduce

I have a *Bump Assembly Versions* project which to this point has worked fine for single target projects. However, in multi-target projects, I am noticing that I may see a *+N* or sometimes a *+N-1* increment, depending on the bump instructions, i.e. like one of the interior platforms unwound its build asynchronously last. This is incorrect, I only want there to be at most a *+1* when there is an increment involved. So... Is there a target I can trigger against that represents the overall build and not each target framework?