Add helper methods for the sound dose test API

Added methods for:
 * getOutputRs2: returns the currently used RS2 value by the audioserver
 * getCsd: returns the current CSD value from the audioserver
 * forceUseFrameworkMel: will enable/disable the computation of the
   MEL values by the framework/HAL
 * forceComputeCsdOnAllDevice: computes CSD for all output playback
   devices.

Test: TestApi
Bug: 248565894
Change-Id: Id34e7e26e57d47ee8ab5a45d08e46b7a3f298ddb