Support to open a project folder in multiple VS Code windows

Problem

Currently VS Code prevents opening a folder more than once which makes it impossible to work on a project in multiple windows (e.g. on multiple displays). @bpasero @dbaeumer @egamma @alexandrudima please raise any obstacles and issues you might foresee with this request. Issues found so far: - [ ] we use the workspace path as identifier to communicate back from debug target to debug host - [ ] we need to verify cross platform that there is no code causing issues when running over the same root folder (e.g. file watchers) --- Please note: Initially I've created this feature request for a specific use case: enable debugging of multiple processes. In the meantime, debugging of multiple processes has become possible without the need for opening a folder more than once (see https://github.com/Microsoft/vscode/issues/13426). But instead of closing this item (as no longer necessary), I've repurposed it by removing the specific debug use case. For transparency you can find the original comment below: > Currently it is not possible to debug more than one process from a single VS Code project (= window) > because VS Code prevents opening a folder more than once. > > The workaround is to open VS code on a subfolder within the original folder, which means to restructure the project (which is not desirable). > > This feature request asks for lifting the constraint and allowing to open a project folder multiple times. >