Sets or gets a slider's step type.
The stepType determines how the slider's steps work:
The step type can be:
"value": Each step's size is the number of units defined by the
step property's value. For example, suppose a slider has a
min value of 0, max value of 10, and
step value of 5. Each step's size will be 5 units, meaning
there will be 2 steps."count": The number of steps is determined by number the units
in the step property's value. For example, suppose a slider
has a min value of 0, max value of 10, and
step value of 5. There will be 5 steps, meaning each step
will be 2 units.