Replace some common index based for loops with for-of loops

Replaces many loops of the form:

```js
for (let i = 0; i < elements.length; ++i) {
    const i = elements[i];
   ...
}
```

with:

```js
for (const element of elements) {
    ...
}
```

Mix of a horrible regex based find/replace and manual touch ups

extensions/vscode-api-tests/src/singlefolder-tests/window.test.ts

@@ -136,8 +136,7 @@ suite('window namespace tests', () => {
 			}).then(() => {
 				assert.equal(actualEvents.length, 2);
 
-				for (let i = 0; i < actualEvents.length; i++) {
-					const event = actualEvents[i];
+				for (const event of actualEvents) {
 					assert.equal(event.viewColumn, event.textEditor.viewColumn);
 				}