Phpstan hasn't identified any errors in Samples in a long time. But, as it turns out, one particular error is suppressed:
```
Variable $helper might not be defined.
```
This error would be generated by almost all samples, and the errors that it suppresses will become problematic if we move to Level 10. We are not yet committed to doing that, but it is pretty easy to write a script to change the samples so that error no longer happens, and there isn't really any reason to delay doing so. The results of that script constitute this PR.
Fix#3951. When an Excel sheet is protected, even when sorting is explicitly allowed without a password, sorts are permitted only on "protected ranges" within the sheet. PhpSpreadsheet already supports protected ranges, and only minor tinkering is necessary for that (e.g. the protected range can have, but does not require, a password). The more important part of this change is documenting the far-from-intuitive way that Excel handles this. To that end, documentation is updated, and a new sample is added.
A new class, `Worksheet\ProtectedRange` is added in place of the string array which had been used. `Worksheet::getProtectedCells` is deprecated in favor of the new `Worksheet::getProtectedCellRanges`.
oleibman