Refactor to improve iterations

- Use function abstractions (such as map, reduce, filter etc.) over
  for-of loops to gain benefits of having less side effects and easier
  readability.
- Enable `downLevelIterations` for writing modern code with lazy evaluation.
- Refactor for of loops to named abstractions to clearly express their
  intentions without needing to analyse the loop itself.
- Add missing cases for changes that had no tests.

tests/unit/stubs/ScriptStub.ts

@@ -13,7 +13,7 @@ export class ScriptStub extends BaseEntity<string> implements IScript {
 
   public readonly documentationUrls = new Array<string>();
 
-  public level = RecommendationLevel.Standard;
+  public level? = RecommendationLevel.Standard;
 
   constructor(public readonly id: string) {
     super(id);
@@ -23,7 +23,7 @@ export class ScriptStub extends BaseEntity<string> implements IScript {
     return Boolean(this.code.revert);
   }
 
-  public withLevel(value: RecommendationLevel): ScriptStub {
+  public withLevel(value?: RecommendationLevel): ScriptStub {
     this.level = value;
     return this;
   }