Replaced PhpExcel with PhpSpreadsheet

[devOp1]

PhpExcel is replaced with PhpSpreadsheet to make yii2-excelexport php8.0 ready. Looking forward for a new version with this PR included.

[mikehaertl]

@devOp1 Thanks for the contribution. I currently have no time to have a closer look.

Did you test that everything still works? I'm actually surprised that there were so little changes. I always thought this would require some bigger refactoring.

In any case the README should also be updated.

Related issue: #24

[devOp1]

@mikehaertl I tested it with a large generated excel with several worksheet. For converting the code i used the rector script from https://phpspreadsheet.readthedocs.io/en/latest/topics/migration-from-PHPExcel/. I am not 100% sure if i configured composer correctly and would like to test that after merging.

[mikehaertl]

@devOp1 Ok, then it's probably fine. Could also go through the README and update the relevant parts (changed class names, link to PHPExcel, maybe update the example to handle styling etc.)? Then I'll merge and create a new release.

[mikehaertl]

@devOp1 Sorry, I forgot a "you" in the question above 😄 . Could you go through the README ...?

Otherwhise I can't promise when I will find time to do it. But I want to keep the README up to date before a release.

[devOp1]

@mikehaertl Done.

[mikehaertl]

@devOp1 Do you need a release or can you do some more testing first?

[devOp1]

I can test without a specific release. Thanks

[mikehaertl]

Cool. Please report back if everything works.

[devOp1]

It's working so far. But i will keep my eyes open.

[mikehaertl]

Ok, I think it's safe to create a release. We can still fix things in a later bugfix release.

Thanks for your help!