[FEATURE] Add support for guards in `switch` statements

[Starexify]

In haxe, we can use guards in switch cases (as documented in the Haxe Manual.

This example code from there:

var myArray = [7, 6];
var s = switch (myArray) {
    case [a, b] if (b > a):
      b + ">" + a;
    case [a, b]:
      b + "<=" + a;
    case _: "found something else";
  }
trace(s); // 6<=7

would return 6<=7 back

But in polymod this isn't supported and errors with this:

 ERROR  Error while parsing script assets/scripts/WorstCParser.hxc#8: EUnexpected
Unexpected error: Unexpected token "if", is there invalid syntax on this line?