VSTACK and HSTACK

[oleibman]

Fix #4485. VSTACK and HSTACK were introduced to Excel in 2024, and will now be supported by PhpSpreadsheet. Special thanks to @SlowFox71, who posted some code to implement VSTACK in the linked issue. I didn't have to change much between that version and the one in this ticket.

Excel has at least one idiosyncrasy with these functions. If you try to stack 2 tables with, say, =VSTACK(TABLE1, TABLE2), Excel will silently change it to =VSTACK(TABLE1[], TABLE2[]) and all will be well. This would be difficult for PhpSpreadsheet to do. The problem is that, when Excel reads the formula without the square brackets, it calculates it as a #NAME? error. This is baffling, and all the more so because you can "correct" it by editing the formula without changing anything, hit enter, and the formula will magically work again. So, if you plan to stack tables using PhpSpreadsheet, you're probably best off using the square brackets.

This is:

• a bugfix
• a new feature
• refactoring
• additional unit tests

Checklist:

• Changes are covered by unit tests
  • Changes are covered by existing unit tests
  • New unit tests have been added
• Code style is respected
• Commit message explains why the change is made (see https://github.com/erlang/otp/wiki/Writing-good-commit-messages)
• CHANGELOG.md contains a short summary of the change and a link to the pull request if applicable
• Documentation is updated as necessary