[docs] Explain how <Alert icon={false} /> behaves (mui#28348)

Co-authored-by: eps1lon <silbermann.sebastian@gmail.com>

docs/translations/api-docs/alert/alert.json

@@ -6,7 +6,7 @@
     "classes": "Override or extend the styles applied to the component. See <a href=\"#css\">CSS API</a> below for more details.",
     "closeText": "Override the default label for the <em>close popup</em> icon button.<br>For localization purposes, you can use the provided <a href=\"/guides/localization/\">translations</a>.",
     "color": "The main color for the alert. Unless provided, the value is taken from the <code>severity</code> prop.",
-    "icon": "Override the icon displayed before the children. Unless provided, the icon is mapped to the value of the <code>severity</code> prop.",
+    "icon": "Override the icon displayed before the children. Unless provided, the icon is mapped to the value of the <code>severity</code> prop. Set to <code>false</code> to remove the <code>icon</code>.",
     "iconMapping": "The component maps the <code>severity</code> prop to a range of different icons, for instance success to <code>&lt;SuccessOutlined&gt;</code>. If you wish to change this mapping, you can provide your own. Alternatively, you can use the <code>icon</code> prop to override the icon displayed.",
     "onClose": "Callback fired when the component requests to be closed. When provided and no <code>action</code> prop is set, a close icon button is displayed that triggers the callback when clicked.<br><br><strong>Signature:</strong><br><code>function(event: React.SyntheticEvent) =&gt; void</code><br><em>event:</em> The event source of the callback.",
     "role": "The ARIA role attribute of the element.",

packages/mui-material/src/Alert/Alert.d.ts

@@ -39,8 +39,9 @@ export interface AlertProps extends StandardProps<PaperProps, 'variant'> {
   /**
    * Override the icon displayed before the children.
    * Unless provided, the icon is mapped to the value of the `severity` prop.
+   * Set to `false` to remove the `icon`.
    */
-  icon?: React.ReactNode | false;
+  icon?: React.ReactNode;
   /**
    * The ARIA role attribute of the element.
    * @default 'alert'

packages/mui-material/src/Alert/Alert.js

@@ -218,6 +218,7 @@ Alert.propTypes /* remove-proptypes */ = {
   /**
    * Override the icon displayed before the children.
    * Unless provided, the icon is mapped to the value of the `severity` prop.
+   * Set to `false` to remove the `icon`.
    */
   icon: PropTypes.node,
   /**