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/assertions.nim

@@ -11,6 +11,7 @@ proc `$`(x: int): string {.magic: "IntToStr", noSideEffect.}
 proc `$`(info: InstantiationInfo): string =
   # The +1 is needed here
   # instead of overriding `$` (and changing its meaning), consider explicit name.
+  result = ""
   result.toLocation(info.filename, info.line, info.column+1)
 
 # ---------------------------------------------------------------------------