[roll] Roll fuchsia [audio][services][mixer] Implement StreamSinkConsumerWriter

This CL adds an implementation of ConsumerStage::Writer that writes
packets to the FIDL StreamSink protocol. The FIDL protocol is abstracted
away by callbacks (`call_put_packet` and `call_end`) and a
`recycled_packet_queue`. The intended flow is:

* The `recycled_packet_queue` is pre-populated with packets, typically
  enough packets to fill the payload VMO(s).

* StreamSinkConsumerWriter pops a packet from `recycled_packet_queue`
  and writes data to that packet. When the packet is full, it's
  forwarded to a FIDL thread via `call_put_packet`.

* A FIDL client implements the `call_put_packet` and `call_end`
  callbacks. These callbacks are translated to PutPacket and End FIDL
  calls, respectively. On each PutPacket call, the client waits for the
  packet to be released, then once released, it adds the packet back
  into `recycled_packet_queue` for use in a future packet.

The FIDL client will be implemented in a follow-up CL.

Original-Bug: 87651
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/719630
Original-Revision: 393b7d1d4419b51daf466597b32163236c29524e
GitOrigin-RevId: 7790b38f4f414e91e23c4a2687e98e520f585099
Change-Id: I08079f33d9cda4c383d623c3993458f276417a5c
diff --git a/stem b/stem
index 3a0a380..fe1d300 100644
--- a/stem
+++ b/stem
@@ -10,7 +10,7 @@
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-             revision="fc1d88c54e827ea18fcb7b2a1c99db4a7a5baa59"/>
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