Enable global effect on Spatializer thread

- APM select spatializer output for music effects when it is active
- mirror mEffectBuffer input/output for AUDIO_SESSION_OUTPUT_MIX session
- return mixerChannelMask for AUDIO_SESSION_OUTPUT_MIX session
- add a helper for stereo spatializer feature enablement check

Flag: EXEMPT bugfix
Bug: 361519000
Test: Enable Visualizer/DynamicsProcessing effect with Clarity
Test: atest CtsMediaAudioTestCases
Change-Id: I366da7bde778040fb8907505760b8e5fc061161d