Dot-sourced reference detection does not account for script blocks

[daviwil]

In PowerShell, it is valid syntax to dot-source a ScriptBlock. Our FindDotSourcedVisitor class does not account for this possibility and treats a dot-sourced ScriptBlock as a referenced script path. This currently does not cause a problem or crash but the behavior should still be fixed.

This issue was originally reported by @itzik-h on the vscode-powershell repo:

PowerShell/vscode-powershell#224 (comment)

[daviwil]

Now tracking this issue on the VS Code side over at PowerShell/vscode-powershell#171.