Passthrough debhelper-compat b-d in dh-update-R
Fixes dh-update-R so that it should work with packages using debhelper-compat (= X) in Build-Depends instead of a d/compat file. The result should use the same style as the original.
Things that could (should?) be done but that aren't in this MR:
- default to
debhelper-compatindh-make-R - automatically convert to
debhelper-compatstyle indh-update-R
See #932179