Upgrade Saxon 9.6.0-2, close #2380
Handle response bodies in recorder
Don't restrict the `bodies` folder to contain request bodies only
Suffix bodies filename with type rather than request id

That allows for better grouping of bodies for a certain request, in
file listing or shell completion.
Dump response bodies (disabled by default)
RawFileBody & ELFileBody can now be used for checks
Extend response bodies flag semantics to imply raw checks
Support base64-encoded content text (HAR 1.2)