Devices that support HDR on one lens but not the other will only allow enabling HDR after restarting the app

[temcguir]

The current code to check for HDR support only checks the front lens at startup, and doesn't update the availability of HDR on the front lens until the app is restarted.

Ideally, all lenses should have their constraints established individually at startup, and only the current lens' constraints should be used when it is in use.