pgsql: Use multibyte-aware extraction of pattern prefixes.

Use multibyte-aware extraction of pattern prefixes.

Previously, like_fixed_prefix() used char-at-a-time logic, which
forced it to be too conservative for case-insensitive matching.

Introduce like_fixed_prefix_ci(), and use that for case-insensitive
pattern prefixes. It uses multibyte and locale-aware logic, along with
the new pg_iswcased() API introduced in 630706ced0.

Reviewed-by: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Reviewed-by: Peter Eisentraut <peter(at)eisentraut(dot)org>
Discussion: https://postgr.es/m/450ceb6260cad30d7afdf155d991a9caafee7c0d.camel@j-davis.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/9c8de1596912b36a8b22d880766ac660b66d03c7

Modified Files
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src/backend/utils/adt/like_support.c | 169 +++++++++++++++++++++++------------
1 file changed, 112 insertions(+), 57 deletions(-)