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/emmet/src/reflectCssValue.ts

@@ -29,9 +29,9 @@ function updateCSSNode(editor: TextEditor, property: Property): Thenable<boolean
 	let currentPrefix = '';
 
 	// Find vendor prefix of given property node
-	for (let i = 0; i < vendorPrefixes.length; i++) {
-		if (property.name.startsWith(vendorPrefixes[i])) {
-			currentPrefix = vendorPrefixes[i];
+	for (const prefix of vendorPrefixes) {
+		if (property.name.startsWith(prefix)) {
+			currentPrefix = prefix;
 			break;
 		}
 	}