hello,
I checked the data sheet also (it doesn't mention it).
You can make some guess. The functional diagram shows mosfets in the ouput and a minimum sink/source current of 2A (at 15V supply).
So the maximum output resistance in this case would be 15/2=7.5 Ohms. In practice, the situation is more complicated. When the mosfet (inside the chip) starts discharging the gate capacitance, it will probably operate more like a current source, when the voltage at the drain (of the mosfet inside the chip), drops sufficiently, it will behave like a resistor (saturated mosfet).
When you are fine with 7.5 Ohms, in reality the discharge and charge of your mosfet gate (fb180a10p) will be faster because of the current source behavior of the output of the chip.
Just assuming the output of the chip is a current source may give a somewhat too optimistic switching time (based on the total gata charge of your mosfet).
If it really matters, best is to measure it with a varying resistive load (under pulsed conditions).
Look to page 13 to know the sink/source current in case of other supply voltage.