Ideas needed: Concise syntax for [System.IO.Path]::Combine()

Combining paths is a common operation in a build system. Now that MSBuild is cross-platform, it's even more fraught with danger due to the vagaries of slash directions.

Most MSBuild projects just use `$(Path1)\$(Path2)`. This works and is concise but has some downsides:
* Has an explicit slash direction
* Can result in doubled slashes (if `Path1` has a trailing slash)
* Isn't obviously a path-combining expression--it's indistinguishable from string concatenation (because that's what it is).

The most-obviously-correct approach is `$([System.IO.Path]::Combine('$(Path1)', '$(Path2)'))`. That doesn't have any of those downsides, but is verbose and hard to read (and type).

It would be great if we could have a concise syntax that called the cross-platform supported system API, but wasn't unreadable. Ideas welcome!