Lexical: Table cell bg and format setting fixes

- Updated table cell background color setting to be stable by
  specifically using the background property over the general styles.
- Updated format shorcuts to be correct header levels as per old editor
  and format menu.
- Updated format changes to properly update UI afterwards.

resources/js/wysiwyg/lexical/table/LexicalTableCellNode.ts

@@ -353,10 +353,17 @@ export function $convertTableCellNodeElement(
   const hasUnderlineTextDecoration = textDecoration.includes('underline');
 
   if (domNode instanceof HTMLElement) {
-    tableCellNode.setStyles(extractStyleMapFromElement(domNode));
+    const styleMap = extractStyleMapFromElement(domNode);
+    styleMap.delete('background-color');
+    tableCellNode.setStyles(styleMap);
     tableCellNode.setAlignment(extractAlignmentFromElement(domNode));
   }
 
+  const background = style.backgroundColor || null;
+  if (background) {
+    tableCellNode.setBackgroundColor(background);
+  }
+
   return {
     after: (childLexicalNodes) => {
       if (childLexicalNodes.length === 0) {