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 same as before.