init checks and 'out' parameters (#14521)

* I don't care about observable stores
* enforce explicit initializations
* cleaner code for the stdlib
* stdlib: use explicit initializations
* make tests green
* algorithm.nim: set result explicitly
* remove out parameters and bring the PR into a mergable state
* updated the changelog

lib/pure/pathnorm.nim

@@ -44,7 +44,7 @@ proc next*(it: var PathIter; x: string): (int, int) =
   it.notFirst = true
 
 iterator dirs(x: string): (int, int) =
-  var it: PathIter
+  var it = default PathIter
   while hasNext(it, x): yield next(it, x)
 
 proc isDot(x: string; bounds: (int, int)): bool =