Android: Ask system for optimal audio buffer size and sample rate

This can reduce audio latency according to
https://developer.android.com/ndk/guides/audio/opensl/opensl-prog-notes#perform.

Previously we were using the hardcoded values of 48000 Hz and 256 frames
per buffer. The sample rate we use with this change is 48000 Hz on all
devices I'm aware of, but the buffer size does vary across devices.

Terminology note: The old code used the term "sample" to refer to what
Android refers to as a "frame". "Frame" is a clearer term to use for
this, so I've changed OpenSLESStream's terminology. One frame consists
of one sample per channel.

Source/Android/jni/AndroidCommon/IDCache.h

@@ -121,4 +121,8 @@ jmethodID GetPermissionHandlerRequestRecordAudioPermission();
 
 jmethodID GetRunnableRun();
 
+jclass GetAudioUtilsClass();
+jmethodID GetAudioUtilsGetSampleRate();
+jmethodID GetAudioUtilsGetFramesPerBuffer();
+
 }  // namespace IDCache