Set the default value of `Config::MAIN_WASAPI_DEVICE` to `default`
instead of `Default`. This fixes an issue where `AudioPane`'s `Output
Device` combo would be blank if `WASAPI` was selected and the user had
never changed the value of `Output Device`.
We don't have to worry about backward compatibility with users who have
`Default` in their config because config values aren't written unless
they've been changed at some point from the default, and the combo has
always saved `default` instead of `Default`.
Audio still worked during emulation in this situation because the
fallback for an unrecognized device name is the default device.
To help prevent similar situations in the future references to
`MAIN_WASAPI_DEVICE`'s default value now call `GetDefaultValue` instead
of hardcoding the expected default, or use the new helper function
`Config::IsDefaultValue`.
Dentomologist
6b2a8eff15