Add OpenAL function for Unigine Engine

+ alSource3i
+ alListener3f
+ alGetEnumValue
+ alSpeedOfSound

The OpenAL part is now working in Unigine Engine.
I can understand adding just stubs for currently non-implemented functions, but they do have an inconveniency of converting linktime warning+runtime abort to linktime+runtime silent ignore. For some codebases, that can lead to difficult-to-debug differences between native and web execution, so I'm not sure if we should allow these kind of silent-to-detect stubs.

Perhaps we should have these kind of functions contain a

    #ifdef OPENAL_DEBUG
    Runtime.warnOnce('alSpeedOfSound() is not yet implemented! Ignoring all calls to it.');
    #endif

of even without the `#ifdef` so that silent behavior will not come to anyone as a surprise?