Media sound is forwarded to PC but not the notifications sound

- [ x] I have read the [FAQ](https://github.com/Genymobile/scrcpy/blob/master/FAQ.md).
- [ x] I have searched in existing [issues](https://github.com/Genymobile/scrcpy/issues).

**Environment**
- OS: [Windows 10]
- scrcpy version: [2.0]
- installation method: [Windows release]
- device model: Google Pixel 5
- Android version: [12]

**Describe the bug**
I get the media sound forwarded to my pc but not the one that comes from the notifications channel, is that already a thing? Is there a way to accomplish such thing?

Reproduce the behavior on Windows 10 with scrcpy 2.0, a Pixel 5, and Android 12, comparing media audio with notification-channel audio. Trace the existing audio-forwarding path and determine whether notification audio can be included; done means notification sounds are forwarded or the limitation is documented.

Written by the indexing model from the issue text.