ScopeManager is inconsistent about path endings #5529

Some parts of ScopeManager require paths to be canonical (ending in "/") -- they concatenate dir names directly to the path, and the code will go into an infinite traversal directory if it receives a path with no trailing "/" (as we learned on the filesystem branch).

Other parts of ScopeManager requires paths to be non-canonical (no trailing "/" at end) -- the code is likely to break if it uses a path with trailing "/" instead. See the two calls to FileUtils.canonicalizeFolderPath() (or stripTrailingSlash(), once #5527 lands), and possibly also three instances of the code dir + "/".

We should clean up ScopeManager so it makes more consistent assumptions about what paths look like.