Doc: reformat catalog/view description tables.
This changes our catalog and view descriptions to use a style inspired
by the new format for function/operator tables: each table entry is
formatted roughly like a <varlistentry>, with the column name and type
on the first line and then an indented description. This provides much
more room for expansive descriptions than we had before, and thereby
eliminates a passel of PDF build warnings.
Discussion: https://postgr.es/m/12984.
1588643549@sss.pgh.pa.us