pgsql: Doc: re-re-revise markup for tables of functions.

Doc: re-re-revise markup for tables of functions.

Make the markup a bit less ad-hoc. A function-table cell now contains
several <para> units, and we label the ones that contain function
signatures with role="func_signature". The CSS or FO stylesheets then
key off of that to decide how to set the indentation. A very useful
win from this approach is that we can have more than one signature
entry per table cell, simplifying the documentation of closely-related
operators and functions.

This patch mostly just replaces the markup in the tables I converted so
far. But I did alter a couple of places where multiple signatures were
helpful.

Discussion: https://postgr.es/m/5561.1587922854@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4ad047a6eac356436b88681a9383a52cde2ffe9c

Modified Files
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doc/src/sgml/func.sgml | 4730 ++++++++++++++++++++++--------------
doc/src/sgml/stylesheet-common.xsl | 7 -
doc/src/sgml/stylesheet-fo.xsl | 35 +-
doc/src/sgml/stylesheet.css | 17 +-
4 files changed, 2962 insertions(+), 1827 deletions(-)