Treating `e1 || e2` as a conditional expression

[panagosg7]

• e1 || e2 ---> let _tmp = e1 in _tmp ? _tmp : e2
• see https://github.com/UCSD-PL/RefScript/blob/fix_lor/tests/pos/operators/lor-00.ts, etc for examples

[ranjitjhala]

Ha, yes -- I guess my suggestion was to just bundle this into the type. Perhaps this is more robust...