aaudio: fix ownership problems with file descriptors

Use unique_fd to track file descriptors.
Fix extra close of file descriptor in SharedMemoryParcelable.cpp.
This bug was causing unrelated file descriptors to be closed!

Bug: 64311216
Test: write_sine.cpp, FD should survive aaudio close
Change-Id: I4f38c83510a49ea22b79b96d970ee48153417249