texlive: changes trigger mass rebuilds

[xeji]

Issue description

Pretty much any change to texlive or its packages triggers a mass rebuild (examples: #46376, #40232), mainly because it is used to build documentation for many packages.

This makes texlive difficult to maintain/bugfix as any change must go through a staging iteration.

My analysis (using maintainers/scripts/rebuild-amount.sh) indicates that the mass rebuild is mainly caused by gtk-doc, which depends on texlive via dblatex.

How can we fix this?

I see 2 possible solutions (of course, any fix will cause a mass rebuild 😄):

1. Build gtk-doc without dblatex by default, which removes the texlive dependency. It won't be able to generate pdf docs, but do we really need them? This is my recommendation.

2. Duplicate texlive as texlive-for-docs and use that for gtk-doc and other packages generating docs. texlive-for-docs won't need frequent updates, it's good enough if it works.

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cc @vcunat @samueldr @jtojnar @pSub @veprbl @bhipple

[vcunat]

1. sounds OK to me. Few people want docs in PDF nowadays, I believe, as few print it and other formats tend to be better on-screen.

Note: 2. wouldn't have to cause a mass rebuild, but I believe we can easily afford a "last" rebuilt this way.

[jtojnar]

👍 for number one – cannot dblatex be added to PATH by peeople who need it?

Also removing dblatex is required for building glib 2.58 docs: #45950 (comment)

[bhipple]

Also 👍 for number 1. In general I'd imagine almost nobody looks at PDF docs by default, and if they do they can just build them.

[xeji]

Should be fixed by #46761 (in staging now).