Revert docs and Storybook changes about target.visibility potential…

…ly not being defined

packages/components/src/number-control/README.md

@@ -106,7 +106,7 @@ The callback receives two arguments:
 1. `newValue`: the new value of the input
 2. `extra`: an object containing, under the `event` key, the original browser event.
 
-Note that the value received as the first argument of the callback is _not_ guaranteed to be a valid value (e.g. it could be outside of the range defined by the [`min`, `max`] props, or it could not match the `step`). In order to check the value's validity, check the `event.target?.validity.valid` property from the callback's second argument (_note: given how the component works internally, the `validity` property is not guaranteed to always be defined on `event.target`. When the `validity` property is not defined, you can assume the value received as valid_).
+Note that the value received as the first argument of the callback is _not_ guaranteed to be a valid value (e.g. it could be outside of the range defined by the [`min`, `max`] props, or it could not match the `step`). In order to check the value's validity, check the `event.target?.validity.valid` property from the callback's second argument.
 
 -   Type: `(newValue, extra) => void`
 -   Required: No

packages/components/src/number-control/stories/index.js

@@ -46,13 +46,7 @@ function Example() {
 				value={ value }
 				onChange={ ( v, extra ) => {
 					setValue( v );
-					// Given how the component works internally, the `validity` property
-					// is not guaranteed to always be defined on `event.target`. When the
-					// `validity` property is not defined, you can assume the value
-					// received as valid.
-					setIsValidValue(
-						extra.event.target.validity?.valid ?? true
-					);
+					setIsValidValue( extra.event.target.validity.valid );
 				} }
 			/>
 			<p>Is valid? { isValidValue ? 'Yes' : 'No' }</p>