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
891180e13d