Replace creating a full Draw component with direct pdfium library calls.
This also means that the result is now a bitmap, not a metafile for now.

Also decouple HAVE_FEATURE_PDFIMPORT and HAVE_FEATURE_PDFIUM, the first
is the "import PDF into Draw" feature, the second is the "insert PDF as
image" feature.

Change-Id: I72c25642ec84cc831df362e02b1520c6e6d9adcf
Reviewed-on: https://gerrit.libreoffice.org/34217Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>