Change data pipe for capture to ReadWriteAudioDataPipe

This is in preparation for an experiment to optimize capture IPC,
which we expect to save a significant amount of CPU and power.
go/input-ipc-optimization

This changes the shared memory used for audio capture from
ReadOnlySharedMemoryRegion to UnsafeSharedMemoryRegion, to allow the
Renderer to write to it. The API changes are in two files:
* media/mojo/mojom/audio_stream_factory.mojom
* media/mojo/mojom/audio_data_pipe.mojom
* media/audio/audio_input_ipc.h
and the rest of the changes follow from those files.

We believe this is safe because:
1) We do not trust or take any sensitive actions based on what is
written in the shared memory. A rogue Renderer, or anyone else writing
to the shared memory, cannot do anything dangerous by writing to it.
2) Audio playout has always used UnsafeSharedMemoryRegion, without
it causing any security issues.

Bug: 380422501
Change-Id: I76a83ff1134b09e83d213e7f609bbec078d4c69b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6038937
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Fredrik Hernqvist <fhernqvist@google.com>
Reviewed-by: Fabian Sommer <fabiansommer@chromium.org>
Reviewed-by: Thomas Guilbert <tguilbert@chromium.org>
Reviewed-by: Mark Foltz <mfoltz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1391519}