[client] usb audio: add microphone recording

Add a composite UAC2 microphone function with its own clock so
recording and playback can use independent sample rates.

Packetize asynchronous capture through usbredir, follow the host
capture clock, and preserve the newest frames across stalls.

Reconfigure active recording without another permission prompt and
fix lost PipeWire capture wakeups.

client/include/interface/audio.h

@@ -120,6 +120,7 @@ typedef struct LG_AudioEventOps
       const void * data, size_t frames,
       const LG_AudioClock * sourceClock);
 
+  /* May repeat with the same generation to update an active stream format. */
   void (*recordStart)(void * opaque, uint32_t generation,
       const LG_AudioFormat * format);
   void (*recordStop)(void * opaque, uint32_t generation);