set flag ShuntingYardParser_debug.

svoid test_ShuntingYardParser() {
  test_ShuntingYardParser(s -> ShuntingYardParser(s/S)!);
}

svoid test_ShuntingYardParser(IF1<S, LS> parse) {
  testFunctionValues(parse,
    "1+2*3",       splitAtSpace_trim("1 2 3 * +"),
    "-3e2",        splitAtSpace_trim("3e2 u-"),
    "-(1+2)",      splitAtSpace_trim("1 2 + u-"),
    "(1+2)-(3+4)", splitAtSpace_trim("1 2 + 3 4 + -"),
  );
}

Began life as a copy of #1032664