Presume the resistors are intended to reduce signal reflections, they may also play a role if ESD protection diodes are present (don't know if). They are surely not intended as short circuit protection, in so far your current and power calculations are inappropriate. Don't think that the involved drivers are capable of continuously supplying 150 mA without damage.
Not applicable in this case. JTAG is operated with high impedance load, voltage drop across series resistors occurs only during signal edge when charging line capacitance, or in an unwanted short circuit condition. As said, it's probably useless to design the resistors for short circuit.