* Add iterateOnlyExistingCells to Constructors
Fix#3721. That issue can already be handled, but requires several statements when one ought to suffice. Adding an extra parameter to the RowCellIterator and ColumnCellIterator constructors is useful, easy, and becomes especially practical now that our supported Php releases all support named parameters (see new test Issue3721Test).
* Update Column.php
* Update .php-cs-fixer.dist.php
* Update Row.php
* Update Column.php
* Update ByColumnAndRowTest.php
oleibman