Avoid using `workspace.rootPath`

[roblourens]

workspace.rootPath is a deprecated property and may not work as expected. Please use workspaceFolders instead. More info: https://github.com/microsoft/vscode/wiki/Adopting-Multi-Root-Workspace-APIs#eliminating-rootpath

microsoft/vscode#69335

[markm77]

Yes, just want to echo that integrated console is opening in root of first (unrelated) project rather than root of project containing script in a multi-root workspace. Which is not desirable but understand you are tracking this.

[TylerLeonhardt]

The problem is, the extension has been working with the assumption that there's one root for so long that switching to mult-root is non-trivial unfortunately.. but we do want to support this.