Add msbuild regression test for native references with spaces

[chamons]

We found a last minute regression in 15.8 that needs tests written to prevent future regressions:

https://devdiv.visualstudio.com/DevDiv/_workitems/edit/649776

Steps to Reproduce

1. Create a new XI project
2. Add a native reference with a space in the path
3. Build with 15.8 and notice failure.

Expected Behavior

No regression from 15.7 in being build-able

Actual Behavior

/Users/donblas/Projects/My App With Spaces/MTOUCH: Error MT0007: The root assembly 'Lib\' does not exist (MT0007) (MyAppWithSpaces)

Build Failed

Environment

15.8 in Beta vs Stable.

Build Logs

https://gist.github.com/chamons/c49975dfc6d1f29db8e680f61fee48cd

Example Project (If Possible)

My App With Spaces.zip

[spouliot]

@rolfbjarne can you confirm that the test you added to PR #4495 covers this ? thanks!

[rolfbjarne]

@spouliot the test I added covers this scenario, but it's XI-only. IMHO it would be nice to have an XM version as well.