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.

src/application/Context/State/Code/Event/CodeChangedEvent.ts

@@ -42,13 +42,12 @@ export class CodeChangedEvent implements ICodeChangedEvent {
 
 function ensureAllPositionsExist(script: string, positions: ReadonlyArray<ICodePosition>) {
   const totalLines = script.split(/\r\n|\r|\n/).length;
-  for (const position of positions) {
-    if (position.endLine > totalLines) {
-      throw new Error(
-        `script end line (${position.endLine}) is out of range.`
-          + `(total code lines: ${totalLines}`,
-      );
-    }
+  const missingPositions = positions.filter((position) => position.endLine > totalLines);
+  if (missingPositions.length > 0) {
+    throw new Error(
+      `Out of range script end line: "${missingPositions.map((pos) => pos.endLine).join('", "')}"`
+        + `(total code lines: ${totalLines}).`,
+    );
   }
 }