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

tests/effects/toutparam.nim

@@ -0,0 +1,28 @@
+discard """
+  cmd: '''nim c --warningAsError[Uninit]:on --skipCfg --skipParentCfg $file'''
+  errormsg: "use explicit initialization of 'x' for clarity [Uninit]"
+  line: 24
+  disabled: "true"
+"""
+
+proc gah[T](x: out T) =
+  x = 3
+
+proc main =
+  var a: array[2, int]
+  var x: int
+  gah(x)
+  a[0] = 3
+  a[x] = 3
+  echo x
+
+main()
+
+proc mainB =
+  var a: array[2, int]
+  var x: int
+  a[0] = 3
+  a[x] = 3
+  echo x
+
+mainB()