Regression - choose lowest-bandwidth codec when the browser can do multiple

[joeyparrish]

I seem to recall that we used to choose codecs based on lowest average bandwidth. Choosing codecs by bandwidth would allow us to prefer, for example, VP9 over H.264 when it would save bandwidth.

Since then, it seems we have regressed. We currently have no way to prefer codecs based on bandwidth. Once the initial selection has been made, we stick with it, but the initial selection is based on available bandwidth only. If there is much bandwidth available, we wind up choosing the least efficient streams.

To reproduce:

1. Load the demo app in Chrome. The demo defaults to the multicodec "Angel One" clip.
2. Open the JS console.
3. Increase the initial bandwidth estimate: debugConfig = { abr: { defaultBandwidthEstimate: Infinity }};
4. Click "load".

The system will choose h.264, even though vp9 could have been played and would have saved bandwidth.

[joeyparrish]

Cherry-picked to v2.1.3.