I (tried to) keep these files consistent locally with astyle in the past,
switching to clang-format makes sure that the recent problem with introducing
inconsistencies in these files doesn't happen again.

(On the flip side, it's great to see that now others also touch this
PDF/pdfium code. :-) )

Change-Id: I6065eab77c584197a82fe48e7d3e81b445106efd
Reviewed-on: https://gerrit.libreoffice.org/51701Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>