Missing default attribute values can cause range input display issues or runtime errors

[danielghost]

As there is no default value for _scaleStart and _scaleEnd, the following error will occur if either are omitted from the JSON:

SliderView.js:35 Uncaught TypeError: Cannot read properties of null (reading 'index')
    at SliderView.getIndexFromValue (SliderView.js:35:13)
    at Slider (slider.jsx:49:25)
    at templates.<computed> (reactHelpers.js:17:19)
    at renderWithHooks (react-dom.development.js:15015:20)
    at mountIndeterminateComponent (react-dom.development.js:17841:15)
    at beginWork (react-dom.development.js:19079:18)
    at HTMLUnknownElement.callCallback (react-dom.development.js:3942:16)
    at Object.invokeGuardedCallbackDev (react-dom.development.js:3991:18)
    at invokeGuardedCallback (react-dom.development.js:4053:33)
    at beginWork$1 (react-dom.development.js:23994:9)

For a confidence slider the runtime error isn't immediately shown, but a missing _scaleStart (if using _linkedToId it will attempt to retrieve these values from the linked model) causes the input display to be out of sync with the value (presumably because it defaults to the default 0 min of <input type="range">. If _scaleEnd is missing the scale is displayed incorrectly and the following error occurs when interacting with the slider:

SliderView.js:35 Uncaught TypeError: Cannot read properties of null (reading 'index')
    at ConfidenceSliderView.getIndexFromValue (SliderView.js:35:13)
    at ConfidenceSliderView.onNumberSelected (ConfidenceSliderView.js:34:24)
    at onChange (confidenceSlider.jsx:190:28)
    at HTMLUnknownElement.callCallback (react-dom.development.js:3942:16)
    at Object.invokeGuardedCallbackDev (react-dom.development.js:3991:18)
    at invokeGuardedCallback (react-dom.development.js:4053:33)
    at invokeGuardedCallbackAndCatchFirstError (react-dom.development.js:4067:27)
    at executeDispatch (react-dom.development.js:8273:5)
    at processDispatchQueueItemsInOrder (react-dom.development.js:8305:9)
    at processDispatchQueue (react-dom.development.js:8318:7)

The schema default for _scaleEnd should also be changed from 1.