chore(lib): update RadioButton

- `RadioButton` migrates to Vue 3. Changes sufficient to render the
  documentation page of `Radio` (including `RadioButton`) are made.
- In `src/components/radio/RadioButton.vue`,
    - `disabled` and `required` are replaced with computed values
      `disabledOrUndefined` and `requiredOrUndefined` respectively,
      that take `true` or `undefined`. Because setting a boolean
      attribute does not remove it on Vue 3, but `null` or `undefined`
      has to be given to remove it.
    - Automatic ESLint fix is applied.

src/components/radio/RadioButton.vue

@@ -4,21 +4,23 @@
             class="b-radio radio button"
             ref="label"
             :class="labelClass"
-            :disabled="disabled"
+            :disabled="disabledOrUndefined"
             @click="focus"
-            @keydown.prevent.enter="$refs.label.click()">
-            <slot/>
+            @keydown.prevent.enter="$refs.label.click()"
+        >
+            <slot />
             <input
                 v-model="computedValue"
                 type="radio"
                 ref="input"
                 @click.stop
-                :disabled="disabled"
-                :required="required"
+                :disabled="disabledOrUndefined"
+                :required="requiredOrUndefined"
                 :name="name"
                 :value="nativeValue"
                 @focus="isFocused = true"
-                @blur="isFocused = false">
+                @blur="isFocused = false"
+            >
         </label>
     </div>
 </template>