Spreadsheet: Add RowIterator::index()

Author: https://github.com/krkk
Commit: f56e240981
Pull-request: https://github.com/SerenityOS/serenity/pull/9576
Reviewed-by: https://github.com/alimpfard

Userland/Applications/Spreadsheet/Readers/XSV.h

@@ -148,6 +148,8 @@ public:
             return m_index == other.m_index && &m_xsv == &other.m_xsv;
         }
 
+        constexpr size_t index() const { return m_index; }
+
     private:
         XSV& m_xsv;
         size_t m_index { 0 };