HLSL: Fix unary and binary operator type conversion issues

This fixes defects as follows:

1. handleLvalue could be called on a non-L-value, and it shouldn't be.

2. HLSL allows unary negation on non-bool values.  TUnaryOperator::promote
   can now promote other types (e.g, int, float) to bool for this op.

3. HLSL allows binary logical operations (&&, ||) on arbitrary types, similar
   (2).

4. HLSL allows mod operation on arbitrary types, which will be promoted.
   E.g, int % float -> float % float.