Summary:
This causes the step to be re-calculated on every update of min, max and step value,
to use the most up to date values for the calculation,
except if step is explicitly set to a non-zero value by the user.
Fixes#10253
**Test plan (required)**
1. Create example app
2. Create a view with a slider that has a `value`, `minimumValue` and `maximumValue` set, but no step value (or step value set to 0).
For example:
```
<Slider
maximumValue={10}
minimumValue={1}
value={4}
/>
```
3. See slider working as expected
Closes https://github.com/facebook/react-native/pull/10343
Differential Revision: D4142646
Pulled By: hramos
fbshipit-source-id: a0df87bbdbbd4b2a291d89f5579f73f517a33dfc