Make requireFiles do less work for larger applications

[misterbyrne]

We have a very large Ember application with loads of modules, so the requireFiles function takes a long time.

This is because the fileSeen array is very long, but only a very small subset of these match the filePattern regex.
The filePattern regex is very simple, but the excludeRegex is more complex. So if we evaluate the simple one first, we'll only have to evaluate the more complex one a much smaller number of times.

I also took the opportunity to simplify the excludeRegex since it's the file extension that we really care about - at the end of the path.

Time spent in requireFiles for one test module of our app before the change was 2605ms, time spent after the change was 70ms.

[patocallaghan]

Thanks @misterbyrne 🙌

[patocallaghan]

Released in 3.9.11