pgsql: Fix parsing of complex morphs to tsquery

Fix parsing of complex morphs to tsquery

When to_tsquery() or websearch_to_tsquery() meet a complex morph containing
multiple words residing adjacent position, these words are connected
with OP_AND operator. That leads to surprising results. For instace,
both websearch_to_tsquery('"pg_class pg"') and to_tsquery('pg_class <-> pg')
produce '( pg & class ) <-> pg' tsquery. This tsquery requires
'pg' and 'class' words to reside on the same position and doesn't match
to to_tsvector('pg_class pg'). It appears to be ridiculous behavior, which
needs to be fixed.

This commit makes to_tsquery() or websearch_to_tsquery() connect words
residing adjacent position with OP_PHRASE. Therefore, now those words are
normally chained with other OP_PHRASE operator. The examples of above now
produces 'pg <-> class <-> pg' tsquery, which matches to
to_tsvector('pg_class pg').

Another effect of this commit is that complex morph word positions now need to
match the tsvector even if there is no surrounding OP_PHRASE. This behavior
change generally looks like an improvement but making this commit not
backpatchable.

Reported-by: Barry Pederson
Bug: #16592
Discussion: https://postgr.es/m/16592-70b110ff9731c07d@postgresql.org
Discussion: https://postgr.es/m/CAPpHfdv0EzVhf6CWfB1_TTZqXV_2Sn-jSY3zSd7ePH%3D-%2B1V2DQ%40mail.gmail.com
Author: Alexander Korotkov
Reviewed-by: Tom Lane, Neil Chen

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/0c4f355c6a5fd437f71349f2f3d5d491382572b7

Modified Files
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src/backend/tsearch/to_tsany.c | 41 ++++++++-
src/test/regress/expected/tsearch.out | 152 +++++++++++++++++-----------------
src/test/regress/sql/tsearch.sql | 36 ++++----
3 files changed, 132 insertions(+), 97 deletions(-)