AttachmentRelationshipFeaturesAvailable function

AttachmentRelationshipFeaturesAvailable loads the selected PDFium module when necessary and returns True when the optional FPDFAttachment_GetAFRelationship entry point is exported

When the export is present, AttachmentRelationship, the Relationship field of TPdfAttachmentMetadata returned by ReadAttachmentMetadata, and the Relationship field filled by TryGetAnnotationFileAttachment report the /AFRelationship name of the file specification (ISO 32000-2 Table 43)

Without the export those values read as an empty string, exactly as they do for a file specification that carries no /AFRelationship entry

• The export is optional so deployments with an older pdfium.dll keep loading; attachment names, descriptions, MIME types and payloads are unaffected
• The Pascal-side writer in FPdfAssocFiles emits the same name tokens (Source, Data, Alternative, Supplement, EncryptedPayload, FormData, Template, Unspecified), so associated files it produces read back through the native API