[examples] Add audio_stream_callback

[dan-hoang]

This is a sister pull request to https://github.com/raysan5/raylib/pull/5637#issue-4054960372.

This commit adds audio_raw_stream_callback.c, which is the same as audio_raw_stream.c in the pull request above, but uses the new API (i.e., SetAudioStreamCallback) instead of the old API (i.e., IsAudioStreamProcessed and UpdateAudioStream).

[raysan5]

@dan-hoang @CrackedPixel I think this example can be redesigned to avoid being mostly a copy of the other one, maybe also renamed to audio_stream_callback and do some processing in the callback? Ideas for a more interesting and appealing example to illustrate callback functionality?

[dan-hoang]

@dan-hoang @CrackedPixel I think this example can be redesigned to avoid being mostly a copy of the other one, maybe also renamed to audio_stream_callback and do some processing in the callback? Ideas for a more interesting and appealing example to illustrate callback functionality?

I'm not an audio guy, so I don't have any good ideas. For now, I just let the user choose between four different waves (sine, square, triangle, and sawtooth), with each wave generated by a different callback. When the user changes the wave they want, the stream's callback is changed appropriately.

I'm thinking that you would do something like this if you have a pipeline of effects set up (like in the stream effects example) and want to swap out the base signal.

[raysan5]

@dan-hoang example looks good, thanks for the improvement