pgsql: Correct docs for the default locale_provider of a new database.

Correct docs for the default locale_provider of a new database.

If the locale provider is not specified, it defaults to be the same as
the template from which it was created. Previously, the documentation
said the default was libc.

Also adjust wording of CREATE DATABASE and CREATE COLLATION docs to be
definite that there are exactly two possible collation providers.

Discussion: https://postgr.es/m/6befdaada61c046b67f3b269f7fa6f069a35803e.camel%40j-davis.com
Reviewed-by: Nathan Bossart

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/a8a44828a2e15c95a15549063205b779f7055f1c

Modified Files
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doc/src/sgml/ref/create_collation.sgml | 10 +++++-----
doc/src/sgml/ref/create_database.sgml  | 10 ++++++----
2 files changed, 11 insertions(+), 9 deletions(-)