Test: new workspace format

[bpasero]

Complexity: 3

• Windows @dbaeumer
• macOS @sandy081
• Linux @mjbvz

We simplified and changed the format of the *.code-workspace files:

• the id property is no longer present. instead, the absolute path of the workspace file is now being used as identifier (so it will change if you move or rename the file)
• the folders entries are now real objects to support additional metadata later
• the folder path property is now just file paths (previously URIs) that can also be relative

To support relative paths in workspace files, a couple of changes went in:

• a relative path is always resolved against the folder (or root if stored in root) where the workspace file is saved to
• when saving a workspace or adding/removing folders, we always save paths as relative paths if possible. a path will be saved as relative when the parent folder of the workspace file is a parent of the root (in other words, we always put the relative path in unless it would result in "../" segments)

A couple of things to verify:

• check the contents of a workspace file make sense to you and is easy to understand
• make copies of a workspace and verify each can be opened into individual windows
• verify that adding/removing folders from within VSCode works properly and updates the path to be relative or absolute depending on the rule described above (no "../" ever)
• verify that saving a workspace to another location converts paths to either relative or absolute depending on the rule described above
• verify paths work cross OS (e.g. each OS can deal with backslash or slash as path segment)
• Windows: verify with special paths
  • UNC paths (\\localhost\c$\my_dir)
  • other drive letters (e.g. D:)