gnu: texlive-libkpathsea: Enforce ls-R usage by default.

Fixes: https://issues.guix.gnu.org/75893

* gnu/packages/tex.scm (texlive-libkpathsea): Set TEXMF so that ls-R database
is mandatory and must contain the file looked after in the TeX Live tree.
* guix/build/texlive-build-system.scm (configure-texmf): Relax requirements
for "ls-R" database.  Renamed from `set-texmfvar'.
(%standard-phases): Apply phase renaming.
* gnu/packages/python-xyz.scm (python-nbconvert)[native-inputs]: Add TeX Live
packages required for tests to pass since propagated packages are no longer
accessible during build.
* gnu/packages/books.scm (book-sparc)[inputs]: Move TeX Live related inputs
to...
[native-inputs]: ... here, and wrap them within texlive-local-tree for the
same reason as above.

Change-Id: I3430bc84ce35f4aa8f0537b512f472ef88f8e5e9

gnu/packages/python-xyz.scm

@@ -19352,7 +19352,28 @@ time.")
            ;; Adding ipywidgets would create a cycle.
            ;;python-ipywidgets
            python-pytest
-           python-pytest-xdist))
+           python-pytest-xdist
+           (texlive-local-tree
+            (list texlive-adjustbox
+                  texlive-booktabs
+                  texlive-caption
+                  texlive-enumitem
+                  texlive-eurosym
+                  texlive-fancyvrb
+                  texlive-float
+                  texlive-fontspec
+                  texlive-grffile
+                  texlive-jknapltx
+                  texlive-parskip
+                  texlive-pdfcol
+                  texlive-rsfs
+                  texlive-soul
+                  texlive-tcolorbox
+                  texlive-titling
+                  texlive-ulem
+                  texlive-unicode-math
+                  texlive-upquote
+                  texlive-xetex))))
     (propagated-inputs
      (list python-beautifulsoup4
            python-bleach