I can't find the file where the angle equivalent of the write.microseconds() function
I don't understand why you're fixated on the "angle" fiction.
If you want 700 to 2000 set it in attach. servo.attach(servoPin,700, 2000).
If I understand things correctly the OP has been given some angle values and he wants to convert them to the appropriate microsecond values.
That won't make 700 be 0 degrees and 2000 be 180 though. It just sets the minimum and maximum values that Servo will put out. The relationship between angle and pulse length is a property of the particular servo you are using.
and that's what the OP seems to be asking for.
The OP doesn't even have a servo. He's got an ESC. ESC doesn't have an angle to it. So it would make a lot more sense to write the pulse width you want