hijriToGregorian method
Implementation
DateTime hijriToGregorian(year, month, day) {
int iy = year;
int im = month;
int id = day;
int ii = iy - 1;
int iln = (ii * 12) + 1 + (im - 1);
int i = iln - 16260;
int mcjdn = id + _ummalquraDataIndex(i - 1)! - 1;
int cjdn = mcjdn + 2400000;
return julianToGregorian(cjdn);
}