FOP subset as at 18 Dec 2020 (post 2.5), https://github.com/apache/xmlgraphics-fop/commit/655ac8ba9dd5fe781c2358051694311bbf21092a
repackaged
then 2 March 2025 copy over enough of https://github.com/apache/xmlgraphics-fop/commit/77cab4884a8a337f23ee7341b69aab62b6880750 for things to compile.
That is FOP 2.10.0-SNAPSHOT which supports PDFBox 3; see https://issues.apache.org/jira/browse/FOP-3203 
