Improve Bank SLM AG PDF-Importer to support exDate (#5741)

- Fix DocumentType declarations to use final var
- Fix regex bug in dividend FX section (spurious > before currency code)
- Fix wrong @Formatter:off tag (should be @Formatter:on)
- Extract ex-date from dividend documents
- Migrate tests to hasItem(purchase/sale/dividend(...)) matcher style

Author: Nirus2000