Table: retain currently selected row when expanding row (#11464)

packages/table/src/table-body.js

@@ -267,7 +267,8 @@ export default {
     },
 
     getRowClass(row, rowIndex) {
-      const classes = ['el-table__row'];
+      const currentRow = this.store.states.currentRow;
+      const classes = currentRow === row ? ['el-table__row', 'current-row'] : ['el-table__row'];
 
       if (this.stripe && rowIndex % 2 === 1) {
         classes.push('el-table__row--striped');