Some clients may care where in the table style list this definition came from, so we'll track it.
The spec only references these by name, unlike Dxf records, which these definitions reference by index
(XML definition order). Nice of MS to be consistent when defining the ECMA standard.
Use org.apache.poi.xssf.usermodel.XSSFBuiltinTableStyle.isBuiltinStyle(TableStyle) to determine whether the index is for a built-in style or explicit user style