Append TargetFramework to *OutputPaths only when MultiTargeting

Rleated issues: #844 #550 #1376 (those github found out)

For single targeting projects, we don’t need to appened the *OutputPaths properties with TargetFramework since, we are only targeting single framework. This is also the behavior of the old projects before sdks were introduced.

1. All the large winforms and wpf projects have custom targets that rely on hard coded paths based on the defaults set by the old project files. It’ll be easy to migrate those projects if those paths were the same. 😌

2. It’ll reduce a directory overhead in the directory tree. One less dir to navigate! 😌

We can update the targets to preserve the old behavior that only appends the TargetFramework property only when it’s multi-targeting.

I can do a PR if you guys are ok with this!

[0xd4d]

It would be a breaking change to change it now. Use the above property instead. If you have many projects you can use a Directory.Build.props file.

[livarcocc]

I disagree in making this breaking change for one kind of project but not for others. I believe differences like that make reasoning about the different project types harder.

There is a property to opt-out of this behavior if someone wants to, but at that point they made that decision explicitly.

Other than that, when you are moving to .net core, this is one of the differences you will have to learn/deal with.