pgsql: Improve some error wording with multirange type parsing

Improve some error wording with multirange type parsing

Braces were referred in some error messages as only brackets (not curly
brackets or curly braces), which can be confusing as other types of
brackets could be used.

While on it, add one test to check after the case of junk characters
detected after a right brace.

Author: Kyotaro Horiguchi
Discussion: https://postgr.es/m/20210514.153153.1814935914483287479.horikyota.ntt@gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/12cc956664f159e97be71e33f15ec5f42e46b24e

Modified Files
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src/backend/utils/adt/multirangetypes.c       | 4 ++--
src/test/regress/expected/multirangetypes.out | 7 ++++++-
src/test/regress/sql/multirangetypes.sql      | 1 +
3 files changed, 9 insertions(+), 3 deletions(-)