RFC: $column->columnIndex() should return "1" instead of "A"

[yob-yob]

PhpSpreadsheet/src/PhpSpreadsheet/Worksheet/Column.php

Lines 42 to 48 in 88bbac9

	/**
	* Get column index as string eg: 'A'.
	*/
	public function getColumnIndex(): string
	{
	return $this->columnIndex;
	}

The Code above should return 1 when column is A

using Coordinate::columnIndexFromString('A')

Why should it return an integer instead of string is because the method is called columnIndex() and this change is for us to be consistent with the definition of index

the Coordinate class defines columnIndex as the index of the column [1 => A, 2 => B, 3 => C, ... ]

we should call A as columnString or columnKey

this is a breaking change so an RFC is needed