Audio effects: Reverb, chrous, delay etc

[fallahn]

https://github.com/SFML/SFML/pull/1708

Implements OpenAL sound effects for reverb, chorus and delay. Can be easily extended to more types supported by OpenAL.
This was discussed some time (10 years!) ago here: https://en.sfml-dev.org/forums/index.php?topic=2245.0 the conclusion being that available OpenAL implementations were not capable. Thankfully things have changed somewhat in the last decade. I've tested this on platforms using openal-soft (windows and ubuntu) and on macOS using Apple's OpenAL library. I was pleasantly surprised to find that the effects are supported by the Apple library, although they are audibly rendered differently - particularly the delay which sounds much softer. However it seems openal-soft is supported on macOS and building SFML against that makes the effects sound consistent across tested platforms. I'm unable to test on mobile platforms.

I'm putting this here to gauge interest - if there's enough feedback I'll add high/low/band pass filters.

[Hapax]

Sounds great!
If they are now available, it makes sense to include them, for sure.