accounting_l10n_fr: Fixes for FEC

This change modifies the FEC export to conform to the test software from
https://www.economie.gouv.fr/dgfip/outil-test-des-fichiers-des-ecritures-comptables-fec 
/ https://github.com/DGFiP/Test-Compta-Demat.

A new `test_compta_demat_compatibility` to enable compatibility mode was introduced.
This will be True when rendering the report from the dialog, i.e., using `AccountingTransactionModule_viewFrenchAccountingTransactionFile` and False when
using `AccountingTransactionModule_viewFrenchAccountingTransactionFileActive` directly
so the behavior of reusing FEC export for accounting interfaces should be the same as before.


See merge request !1764