Support amplitude (dBFS) on Linux

[matthiasn]

Is your feature request related to a problem? Please describe.

I use this library in a multi-platform app and I'm used to see the audio levels visualized in a VU meter I've created for this purpose, and while not accurate or technically useful like a VU meter in recording studio settings, it does make the UI feel more alive, and immediately shows when something is off, as the needle simply won't move when input is muted or whatnot.

However, with the amplitude not implemented on Linux, it makes the audio UX in the Linux version feel dead and broken.

Describe the solution you'd like

Ideally, the library would simply support amplitude on Linux in a similar way as it does on all other platforms.

Describe alternatives you've considered

An alternative could be to find another audio recording library specifically for Linux, or replace the use of this library altogether.

[matthiasn]

Also see matthiasn/lotti#2181 to track fixing VU meter support on Linux.