Changed interpolateNoteX to be a bit faster

[DJLuna441]

It's about 15-20% faster than the old one.
The test was:

function DEBUG_RunTest(){
 let start = performance.now();
 for(let i = 0; i < 120; i+=0.000001){
  interpolateNoteX(i); //The Old One
 }
 let end = performace.now();
 let oldTime = end - start;
 start = performance.now();
 for(let i = 0; i < 120; i+=0.000001){
  newInterpolateNoteX(i); //The New One
 }
 end = performace.now();
 let newTime = end - start;
 console.log("New: " + newTime + " | Old: " + oldTime);
}

Under those (quite unrealistic imo) circumstances the new One is faster. In my oppinion the new implementation is not worth the performace gain since its quite unreadable now since math is not as overviewable than a lerp and a map.