More manual conversion of index based for loops to for-of loops

make font platform specific for different languages, https://github.com/Microsoft/vscode/pull/65776#issuecomment-451225090

- Cursor flickering in powershell is _really_ annoying and there is no way
  to work around it reliably. It's happening because conpty hides and shows
  the cursor many times when it doesn't really need to, and since data isn't
  batched xterm.js renders as much as possible which shows the cursor in
  positions.
- Kill doesn't kill the process, this is likely a problem on our end.

Part of #66001

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

Casts can hide some type errors

Don't use `Function` as it allows any sort of calling pattern

Calling `fire` with zero arguments results in the emitter firing with `undefined`. This is often not expected or desired. It should be explicit that the emitter is fired with undefined

Fixed an issue where open keybindings icon disappears in the keybindings editor view by setting tab index to -1