Workspace path parsing fails on Windows

**Type of issue**: Bug Report

**Please provide the steps to reproduce the problem:**

1. clone chisel template
2. run `sbt test`
3. it fails

**What is the current behavior?**

I traced it down to this:
`EphemeralSimulator.makeSimulator` creates a Simulator with workspace path that starts with "C:\", then when parsing this temp dir at https://github.com/chipsalliance/chisel/blob/ce05462c239deec8aee0704efbd3a71e8b64ec49/svsim/src/main/scala/Workspace.scala#L32, it is mistakenly considered as a relative path which leads to errors.

**What is the expected behavior?**

Maybe we can find a way that is more friendly to Windows? For example add `|| path(1) == ':'`.

**Please tell us about your environment:**

- version: `6.2.0`
- OS: Windows with msys2 environment

**Other Information**

**What is the use case for changing the behavior?**

To run it on Windows.

Acutally I'm not sure if chisel is intended not to support Windows. I didn't see any warnings about this. If so, please tell me.