mirabilos authored Jan 20, 2022 and mirabilos committed Jan 20, 2022

add qdf-based workaround for the PDF page group problems
(tested in buster (edugit pubmat builder) and bullseye)

This addresses pdf{,la}tex warnings relating including PDFs as
graphics: Inkscape adds a “page group”, which is necessary for
transparency, but there may only ever be one page group, and
for the (final) result PDF we need the one from pdftex, and it
only inserts the proper one if there was none, otherwise the
one from the first included PDF that had one gets used, which
might not match the pdftex output.

There’s no programmatic way around that: while we can output a
proper page group in the .tex/.sty/.cls file manually, this
does not inhibit the (possibly wrong) one from the first included
PDF being copied, ending up with a bad PDF.

There’s only one proper fix: a̲l̲l̲ PDFs included in a pdfTₑχ/LᴬTᴇΧ
document m̲u̲s̲t̲ have their page group stripped. (Unfortunately,
pdf{,la}tex only warns if at least two have one.)

This commit implements the stripping for those PDFs we generate
out of SVG files via Inkscape. (It also drops the Producer info,
which is uselessly taking up space.)