A reference to a worksheet as declared in xl/workbook.xml.
The rel_id resolves against xl/_rels/workbook.xml.rels to produce the
actual package path of the sheet (typically xl/worksheets/sheet*.xml).
Summary
Types
@type state() :: :visible | :hidden | :very_hidden
@type t() :: %ExVEx.OOXML.Workbook.SheetRef{ name: String.t(), rel_id: String.t(), sheet_id: pos_integer(), state: state() }