pgsql: Support index INCLUDE in the AM properties interface.

Support index INCLUDE in the AM properties interface.

This rectifies an oversight in commit 8224de4f4, by adding a new
property 'can_include' for pg_indexam_has_property, and adjusting the
results of pg_index_column_has_property to give more appropriate
results for INCLUDEd columns.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/49b0e300f7dd56b092c0046ee29dc2b15beea9a8

Modified Files
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doc/src/sgml/func.sgml                |   6 ++
src/backend/utils/adt/amutils.c       | 158 +++++++++++++++++++++++-----------
src/include/access/amapi.h            |   9 +-
src/test/regress/expected/amutils.out |  57 ++++++++++--
src/test/regress/sql/amutils.sql      |  17 +++-
5 files changed, 185 insertions(+), 62 deletions(-)