XLSX export should be provided

[yann-papouin]

This new MS Excel file format (Office 2007) is able to extend the built-in limits of the XLS file format and would allow to provide a workaround for the 65535 row limit.

Possible migration to openpyxl (or XlsxWriter) and xlsx/xlsb.

[jmcnamara]

Added an initial pull request for this feature.

[nhomar]

This is working since few time ago (> 9.0)

[mlaitinen]

@nhomar What do you mean it's "working since few time ago"? I'm checking the 12.0 and master source code and Odoo is still using the xlwt library that only produces .xls files, not .xlsx.

Yes, it's possible to import .xlsx files, but not to export them.

It's 2019. I don't see a reason to support Excel 2003 format anymore.

Seems like #32339 is our best bet.