pgsql: Address more review comments on commit 2d819a08a1.

Address more review comments on commit 2d819a08a1.

Based on comments from Peter Eisentraut.

 * Document CREATE DATABASE ... BUILTIN_LOCALE.
 * Determine required encoding based on locale name for CREATE
   COLLATION. Use -1 for "C" (requires catversion bump).
 * initdb output fixups.
 * Make ctype_is_c a constant true for now.
 * Fixups to ICU 010_create_database.pl test.

Discussion: https://postgr.es/m/4135cf11-206d-40ed-96c0-9363c1232379@eisentraut.org

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/846311051e8fdca4c9db83b2b09425759a8b102d

Modified Files
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doc/src/sgml/ref/create_database.sgml | 18 ++++++++++++++++++
src/backend/commands/collationcmds.c  |  2 +-
src/backend/utils/adt/pg_locale.c     | 28 +++++++++++++++++++++-------
src/bin/initdb/initdb.c               |  7 ++++---
src/bin/initdb/t/001_initdb.pl        |  2 +-
src/include/catalog/catversion.h      |  2 +-
src/include/utils/pg_locale.h         |  1 +
src/test/icu/t/010_database.pl        | 12 +++++++++++-
8 files changed, 58 insertions(+), 14 deletions(-)