[IMP] website: ease the header and footer visibility management

This commit doesn't introduce any functional change but allows to manage
header and footer visibility with the already existing data-invisible
system. This simplifies the code and avoids doing an RPC at the start of
the `VisibilityPageOptionUpdate` option.

Related to opw-2971181

closes odoo/odoo#107387

X-original-commit: 07fdbc8847d254498b908a1cde0d910a77666f25
Related: odoo/upgrade#4120
Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

addons/website/static/src/js/editor/snippets.options.js

@@ -2255,14 +2255,6 @@ const VisibilityPageOptionUpdate = options.Class.extend({
     showOptionWidgetName: undefined,
     shownValue: '',
 
-    /**
-     * @override
-     */
-    async start() {
-        await this._super(...arguments);
-        const shown = await this._isShown();
-        this.trigger_up('snippet_option_visibility_update', {show: shown});
-    },
     /**
      * @override
      */

addons/website/views/website_templates.xml

@@ -206,9 +206,11 @@
     </xpath>
     <xpath expr="//header" position="attributes">
         <attribute name="t-attf-class" add="#{'d-none o_snippet_invisible' if 'header_visible' in main_object and not main_object.header_visible else ''}" separator=" "/>
+        <attribute name="t-att-data-invisible">'1' if 'header_visible' in main_object and not main_object.header_visible else None</attribute>
     </xpath>
     <xpath expr="//footer[@id='bottom']" position="attributes">
         <attribute name="t-attf-class" add="#{'d-none o_snippet_invisible' if 'footer_visible' in main_object and not main_object.footer_visible else ''}" separator=" "/>
+        <attribute name="t-att-data-invisible">'1' if 'footer_visible' in main_object and not main_object.footer_visible else None</attribute>
     </xpath>
 </template>