pgsql: Add hash support functions and hash opclass for contrib/ltree.

Add hash support functions and hash opclass for contrib/ltree.

This also enables hash join and hash aggregation on ltree columns.

Tommy Pavlicek, reviewed by jian he

Discussion: https://postgr.es/m/CAEhP-W9ZEoHeaP_nKnPCVd_o1c3BAUvq1gWHrq8EbkNRiS9CvQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/485f0aa85995340fb62113448c992ee48dc6fff1

Modified Files
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contrib/ltree/Makefile            |  3 +-
contrib/ltree/expected/ltree.out  | 68 ++++++++++++++++++++++++++++++++++++++
contrib/ltree/ltree--1.2--1.3.sql | 23 +++++++++++++
contrib/ltree/ltree.control       |  2 +-
contrib/ltree/ltree_op.c          | 69 +++++++++++++++++++++++++++++++++++++++
contrib/ltree/ltreetest.sql       |  1 +
contrib/ltree/meson.build         |  3 +-
contrib/ltree/sql/ltree.sql       | 47 ++++++++++++++++++++++++++
doc/src/sgml/ltree.sgml           |  8 +++++
9 files changed, 221 insertions(+), 3 deletions(-)