[FIX] website: copy frontend link when using the anchor option

Before this commit, clicking on the "anchor" icon from a snippet editor
would copy the client action's url (introduced in [1]).

This commit changes the snippet's path computation to use the target's
ownerDocument location instead of the global one.

[1]: https://github.com/odoo/odoo/commit/31cc10b91dc7762e23b4bde9b945be0c4ce3fe3b

task-2687506

Part-of: odoo/odoo#96401

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

@@ -2458,7 +2458,7 @@ options.registry.anchor = options.Class.extend({
             }
             this._setAnchorName(anchorName + n);
         }
-        return `${window.location.pathname}#${this.$target[0].id}`;
+        return `${this.ownerDocument.location.pathname}#${this.$target[0].id}`;
     },
     /**
      * Creates a safe id/anchor from text.

addons/website/static/tests/tours/snippet_editor_panel_options.js

@@ -42,4 +42,35 @@ wTourUtils.dragNDrop({
             console.error("The paragraph text selection was lost.");
         }
     },
+}, {
+    content: "Click on the anchor option",
+    trigger: '#oe_snippets .snippet-option-anchor we-button',
+    run() {
+        // The clipboard cannot be accessed from a script.
+        // https://w3c.github.io/editing/docs/execCommand/#dfn-the-copy-command
+        // The execCommand is patched for that step so that ClipboardJS still
+        // sends the 'success' event.
+        const oldExecCommand = document.execCommand;
+        document.execCommand = () => true;
+        this.$anchor[0].click();
+        document.execCommand = oldExecCommand;
+    }
+}, {
+    content: "Check the copied url from the notification toast",
+    trigger: '.o_notification_manager .o_notification_content',
+    run() {
+        const { textContent } = this.$anchor[0];
+        const url = textContent.substring(textContent.indexOf('/'));
+
+        // The url should not target the client action
+        if (url.startsWith('/@')) {
+            console.error('The anchor option should target the frontend');
+        }
+
+        const iframeDocument = document.querySelector('.o_iframe').contentDocument;
+        const snippetId = iframeDocument.querySelector('.s_text_image').id;
+        if (!url || url.indexOf(snippetId) < 0) {
+            console.error('The anchor option does not target the correct snippet.');
+        }
+    },
 }]);