Copied references do not get cleaned when output is not under project directory

Copied assembly references (including those from NuGet packages) are added to `@(FileWritesShared)` and only go into `@(FileWrites)` to be cleaned later if they're written to a [subdirectory of the project folder](https://github.com/Microsoft/msbuild/blob/9354c727bd70450912c882dfeaf8941a67dc2f66/src/Tasks/Microsoft.Common.CurrentVersion.targets#L4757-L4769).

That causes them to never be cleaned if the user project redirected the output of a project, even if that output isn't shared with other projects.