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/application/Context/State/Code/ApplicationCode.spec.ts

@@ -197,7 +197,7 @@ class UserScriptGeneratorMock implements IUserScriptGenerator {
     selectedScripts: readonly SelectedScript[],
     scriptingDefinition: IScriptingDefinition,
   ): IUserScript {
-    for (const [parameters, result] of Array.from(this.prePlanned)) {
+    for (const [parameters, result] of this.prePlanned) {
       if (selectedScripts === parameters.scripts
         && scriptingDefinition === parameters.definition) {
         return result;

tests/unit/application/Context/State/Code/Event/CodeChangedEvent.spec.ts

@@ -13,16 +13,23 @@ describe('CodeChangedEvent', () => {
       it('throws when code position is out of range', () => {
         // arrange
         const code = 'singleline code';
+        const nonExistingLine1 = 2;
+        const nonExistingLine2 = 31;
         const newScripts = new Map<SelectedScript, ICodePosition>([
-          [new SelectedScriptStub('1'), new CodePosition(0, 2 /* nonexisting line */)],
+          [new SelectedScriptStub('1'), new CodePosition(0, nonExistingLine1)],
+          [new SelectedScriptStub('2'), new CodePosition(0, nonExistingLine2)],
         ]);
         // act
-        const act = () => new CodeChangedEventBuilder()
-          .withCode(code)
-          .withNewScripts(newScripts)
-          .build();
+        let errorText = '';
+        try {
+          new CodeChangedEventBuilder()
+            .withCode(code)
+            .withNewScripts(newScripts)
+            .build();
+        } catch (error) { errorText = error.message; }
         // assert
-        expect(act).to.throw();
+        expect(errorText).to.include(nonExistingLine1);
+        expect(errorText).to.include(nonExistingLine2);
       });
       describe('does not throw with valid code position', () => {
         // arrange