Audio policy: selectively enable binaural or transaural stereo spatialization

Use two system properties to selectively enable transaural or binaural
stereo spatialization:
- if ro.audio.stereo_spatialization_enabled is true, enable stereo
  spatialization independently of device category
- if ro.audio.stereo_spatialization_enabled is false or not defined,
enable stereo spatialization if:
- ro.audio.stereo_spatialization_binaural_enabled is true and the device
is in the headphones category
- ro.audio.stereo_spatialization_transaural_enabled is true and the device
is in the speaker category

Bug: 417494541
Flag: com.android.media.audio.stereo_spatialization_binaural_transaural
Test: manual verification of all properties combinations
Test: atest audiopolicy_tests
Test: atest spatializer_tests
Test: atest android.media.audio.cts.SpatializerTest
Change-Id: I221b31ddc648ee1c573b3d73386feb09df925a53