Implement audio effects HAL delegating to legacy HAL

Changes made to the .hal definition:

  - added missing generated Result for methods implemented via legacy
    "command" function;

  - fixed Aux Channels feature definition;

  - added "size" parameter for reply data in cases where the wrapper
    needs to allocate a reply buffer;

  - added method for generic support of feature configs;

  - added new Result type;

  - use arrays instead of strings in effect descriptor to ease
    conversion from / to legacy HAL;

  - added missing method to the Preset Reverb interface;

  - fixed names of the Visualizer enums to avoid clashes with defines
    from the legacy HAL file.

The implementation isn't hooked up to the server yet. Need to implement
devices and streams first.

Bug: 30222631
Change-Id: I75bb42f19ac3303759e918b6d6a91646b1555f8c
Test: make