Api4 - Use explicit adder functions rather than magicMethod

Api4 - Use explicit adder functions rather than magicMethod

Api Actions had been relying on a magic method to provide getter/setter functions for params.
That works fine for simple get/set operations but it was also attempting to provide adder functions.
Those are more nuanced and the magic method didn't do a good job of understanding whether the param
was an indexed or unindexed array, and didn't do strict type checking.
Making our own adder functions gives better documentation, stricter checking of inputs and also
the convenience of variadic functions for adding several values at once.