PowerPreference::Default will now prefer discrete GPUs
when on AC power and will prefer integrated GPUs while
on battery power (i.e. the battery is discharging).
Get the examples running again.
The compute example has been simplified to use only one buffer.
A new check has been added to ensure the `max_bind_groups`
device limit is properly set.
This PR removes optional backend features in favor of run-time
selection at the `request_adapter` entry point. Adapters from all
supported gpu backends on the platform are reported.
It also makes gfx-rs dependency to be public (for now).
