Data Exchange, STEP - use std::string_view for STEP type names and API (#784)

Data Exchange, STEP - use std::string_view for STEP type names and API (#784)

- Replace many static TCollection_AsciiString recognition constants with
  constexpr std::string_view (Reco_*, s_* short names) and include <string_view>.
- Change StepType() API to return const std::string_view& in
  StepData_ReadWriteModule and related modules (RWHeaderSection, RWStepAP214).
- Convert typenums/typeshor maps to use std::string_view keys and lazy
  initialization via initializeTypenums/initializeTypeshor + getTypenums/getTypeshor.
- Update call sites to adapt to new return type (wrap into TCollection_AsciiString
  where a TCollection_AsciiString is required).
- Minor refactoring to headers to add <string_view> includes and keep thread-safe
  singleton initialization for the maps.