Another fix for workspace path joining

[dylni]

This is an alternative to #8874 without using Path::components as a hack.

[rust-highfive]

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[ehuss]

Closing as this PR is quite old, and unfortunately it isn't entirely clear on how to proceed with fixing the Windows paths issues (and unfortunately none of us have much time to invest in this). I have opened #9769 as a meta issue to cover this. I understand this can be a frustrating issue to deal with, and this isn't saying we don't want it fixed (we very much do!), but that we want to better understand how to proceed. Thanks!