[FIX] web_editor: move rules cache from document to wysiwyg instance

The CSS rules cache for convert_inline was stored on the edited
document, which is problematic since OWL destroys the document where we
used to just hide it (eg, when switching tabs in the form view).

X-original-commit: d432ebbddae7192eca7215a8489abb3ad91a45f2
Part-of: odoo/odoo#111778

addons/web_editor/static/src/js/backend/convert_inline.js

@@ -552,11 +552,14 @@ async function toInline($editable, cssRules, $iframe) {
     $editable.removeClass('odoo-editor-editable');
     const editable = $editable.get(0);
     const iframe = $iframe && $iframe.get(0);
+    const wysiwyg = $editable.data('wysiwyg');
     const doc = editable.ownerDocument;
-    cssRules = cssRules || doc._rulesCache;
+    cssRules = cssRules || wysiwyg && wysiwyg._rulesCache;
     if (!cssRules) {
         cssRules = getCSSRules(doc);
-        doc._rulesCache = cssRules;
+        if (wysiwyg) {
+            wysiwyg._rulesCache = cssRules;
+        }
     }
 
     // If the editable is not visible, we need to make it visible in order to

addons/web_editor/static/src/js/wysiwyg/wysiwyg.js

@@ -2548,6 +2548,7 @@ const Wysiwyg = Widget.extend({
         }
         const {collaborationChannel} = this.options;
         this._stopPeerToPeer();
+        this._rulesCache = undefined; // Reset the cache of rules.
         // If there is no collaborationResId, the record has been deleted.
         if (!collaborationChannel || !collaborationChannel.collaborationResId) {
             this.setValue(value);