pgsql: docs: html: load stylesheet via custom.css.source

docs: html: load stylesheet via custom.css.source

Until now the meson built docs did not have a working reference to the css
stylesheet, it was copied in the make target. Instead of duplicating that for
meson, use the docbook-xsl parameter custom.css.source to reference it. An
additional benefit of that approach is that the stylesheet is now included in
the single-file HTML documentation.

Reported-by: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Discussion: https://postgr.es/m/3fc3bb9b-f7f8-d442-35c1-ec82280c564a@enterprisedb.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/b8059bdf1ef8f7e215ec5010fcf6c3bd9c491eef

Modified Files
--------------
doc/src/sgml/Makefile                    |  3 +--
doc/src/sgml/meson.build                 |  2 +-
doc/src/sgml/stylesheet-html-common.xsl  |  8 ++++++++
doc/src/sgml/stylesheet-html-nochunk.xsl |  3 +++
doc/src/sgml/stylesheet.css.xml          |  8 ++++++++
doc/src/sgml/stylesheet.xsl              | 11 -----------
6 files changed, 21 insertions(+), 14 deletions(-)