pgsql: Simplify code for getting a unicode codepoint's canonical class.

Simplify code for getting a unicode codepoint's canonical class.

Three places of unicode_norm.c use a similar logic for getting the
combining class from a codepoint.  Commit 2991ac5 has added the function
get_canonical_class() for this purpose, but it was only called by the
backend.  This commit refactors the code to use this function in all
the places where the combining class is retrieved from a given
codepoint.

Author: John Naylor
Discussion: https://postgr.es/m/CAFBsxsHUV7s7YrOm6hFz-Jq8Sc7K_yxTkfNZxsDV-DuM-k-gwg@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/16c302f51235eaec05a1f85a11c1df04ef3a6785

Modified Files
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src/common/unicode_norm.c | 47 ++++++++++++++++++++++-------------------------
1 file changed, 22 insertions(+), 25 deletions(-)