* fixed#16938: Audio could not be played entirely on iOS/macOS. And refactored some code of decoding.
* Adds license header, removes unused macros.
* issue #16938: Corrects remaining frame count calculation.
* Updates include path.
* Adds comments for AudioDecoder class.
* Adds const for getter functions in AudioDecoder.
* issue #16938: Adds test case.
* Updates license years.
* Deletes trailing white spaces.
* [audio] Fixes some issues while stop/uncache right after play/preload on OSX/iOS platform.
* Better state control in AudioCache.
* Adds State enum class which contains INITIAL, LOADING, READY, FAILED states.
* AudioPlayer::destroy should check AudioCache::_isAudioLoaded flag, otherwise, app will freeze in cpp-tests/NewAudioEngineTest/6:Test invalid audio file.
* Should check whether state is INITIAL in the destructor of AudioCache.
* Adds test case for switching play state frequently.
* Skips invoking reading data callback if cache's state is INITIAL.
* Variables initialization for AudioCache class and fixes protential missing delete AL buffers.
James Chen