AAudio: add a limiter instead of clipping audio

AAudio currently clips audio above sqrt(2) and below -sqrt(2).
Instead, for a smooth transition, a polynomial spline should be used.

Bug: 17914011
Test: atest test_flowgraph
Test: atest AAudioTests
Test: Test Output in OboeTester
Change-Id: Ia48537c9c914b71f6928adfc2470f17b3108e5d5