* Order book was about $7.85 billion from 250 accounts* Sukuk issued at a profit rate of 3.764 percent* Priced within Dubai 2023 sukuk* Investors see firm backing for Sharjah from Abu Dhabi* Prosperity from south of UAE spilling into north(Adds details, quotes, data)By Archana NarayananDUBAI, Sept 10 (Reuters) - The emirate of Sharjah attracted massive demand at its first international debt sale o