pgsql: Add strict_word_similarity to pg_trgm module

Add strict_word_similarity to pg_trgm module

strict_word_similarity is similar to existing word_similarity function but
it takes into account word boundaries to compute similarity.

Author: Alexander Korotkov
Review by: David Steele, Liudmila Mantrova, me
Discussion:
https://www.postgresql.org/message-id/flat/CY4PR17MB13207ED8310F847CF117EED0D85A0@CY4PR17MB1320.namprd17.prod.outlook.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/be8a7a6866276b228b4ffaa3003e1dc2dd1d140a

Modified Files
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contrib/pg_trgm/Makefile                         |    5 +-
contrib/pg_trgm/expected/pg_strict_word_trgm.out | 1025 ++++++++++++++++++++++
contrib/pg_trgm/pg_trgm--1.3--1.4.sql            |   68 ++
contrib/pg_trgm/pg_trgm.control                  |    2 +-
contrib/pg_trgm/sql/pg_strict_word_trgm.sql      |   42 +
contrib/pg_trgm/trgm.h                           |   21 +-
contrib/pg_trgm/trgm_gin.c                       |    9 +-
contrib/pg_trgm/trgm_gist.c                      |   14 +-
contrib/pg_trgm/trgm_op.c                        |  248 +++++-
doc/src/sgml/pgtrgm.sgml                         |   88 +-
10 files changed, 1461 insertions(+), 61 deletions(-)