aaudio: set to SHARED when EXCLUSIVE fails

SHARED streams and endpoints were being created with sharing mode
set to EXCLUSIVE. This was confusing the close() code and caused a hang.

Now we create a modified Request object with the sharing mode set
correctly.

Bug: 112709847
Test: Hack AAudioServiceEndpointMMAP so isBufferShareable is false.
Test: 'adb shell write_sine_callback -pl -x -s2' should not hang.
Change-Id: I7a5c8260beaffdd706f34d35ef00a61b072adb1d