doc: Rework tables for built-in operator classes of index AMs

doc: Rework tables for built-in operator classes of index AMs

The tables listing all the operator classes available for BRIN, GIN,
GiST and SP-GiST had a confusing format where the same operator could be
listed multiple times, for different data types.  This improves the
shape of these tables by adding the types associated to each operator,
for their associated operator class.

Each table included previously the data type that could be used for an
operator class in an extra column.  This is removed to reduce the width
of the tables as this is now described within each operator.  This also
makes the tables fit better in the PDF documentation.

Reported-by: osdba
Author: Michael Paquier
Reviewed-by: Álvaro Herrera, Tom Lane, Bruce Momjian
Discussion: https://postgr.es/m/38d55061.9604.173b32c60ec[email protected]