Effects: add a method to retrieve audio configuration

An effect can be instantiated on different streams,
which affects its configuration. For some audio effects
like Visualizer it's important to know the sampling
rate that the effect operates on. The new method
provides means for retrieving current audio configuration
of the effect.

Bug: 162727518
Test: atest CtsMediaAudioTestCases:VisualizerTest
Change-Id: I2390dd07a67d1eaf4ed92a911d8a2c4b2e083027