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/system/widestrs.nim

@@ -63,6 +63,7 @@ proc ord(arg: Utf16Char): int = int(cast[uint16](arg))
 proc len*(w: WideCString): int =
   ## returns the length of a widestring. This traverses the whole string to
   ## find the binary zero end marker!
+  result = 0
   while int16(w[result]) != 0'i16: inc result
 
 const