pgsql: Account for collation when coercing the output of a SQL function

Account for collation when coercing the output of a SQL function.

Commit 913bbd88d overlooked that the result of coerce_to_target_type
might need collation fixups.  Per report from Andreas Joseph Krogh.

Discussion: https://postgr.es/m/VisenaEmail.72.37d08ec2b8cb8fb5.17179940cd3@tc7-visena

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/2d59643dbccaf73bc1f90875ea02dcad641379cd

Modified Files
--------------
src/backend/executor/functions.c      |  3 +++
src/test/regress/expected/collate.out | 15 ++++++++++++++-
src/test/regress/sql/collate.sql      |  8 ++++++++
3 files changed, 25 insertions(+), 1 deletion(-)