Update phpoffice/phpspreadsheet to v2

[karstennilsen]

• Update dependency
• Replace depricated function setCellValueByColumnAndRow
• htmlHelper->toRichTextObject does not support null anymore, convert null to empty string

Improvement / replacement of https://github.com/omines/datatables-bundle/pull/329

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 94.45%. Comparing base (2c41aae) to head (989c450).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #330 +/- ## ======================================= Coverage 94.45% 94.45% ======================================= Files 36 36 Lines 956 956 ======================================= Hits 903 903 Misses 53 53 ```

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[curry684]

Looks legit 👍

Keep in mind that this is technically a BC break and so will not be autoupdated without manually changing your dependency.

[curry684]

Turns out your change doesn't break on v1 so we can support both.