WYSIWYG: Code & table fixes

- Fixed new code block insertion to remove selection area instead of
  just adding after.
- Added default table column widths to not be collapsed
- Updated table dom export to not duplicate colgroups.

resources/js/wysiwyg/ui/framework/blocks/table-creator.ts

@@ -74,8 +74,12 @@ export class EditorTableCreator extends EditorUiElement {
             return;
         }
 
+        const targetColWidth = Math.min(Math.round(840 / columns), 240);
+        const colWidths = Array(columns).fill(targetColWidth + 'px');
+
         this.getContext().editor.update(() => {
             const table = $createTableNodeWithDimensions(rows, columns, false) as CustomTableNode;
+            table.setColWidths(colWidths);
             $insertNewBlockNodeAtSelection(table);
         });
     }