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/typetraits.nim

@@ -112,7 +112,7 @@ macro genericParamsImpl(T: typedesc): untyped =
       of nnkBracketExpr:
         for i in 1..<impl.len:
           let ai = impl[i]
-          var ret: NimNode
+          var ret: NimNode = nil
           case ai.typeKind
           of ntyTypeDesc:
             ret = ai