pgsql: Allow => syntax for named cursor arguments in plpgsql.

Allow => syntax for named cursor arguments in plpgsql.

We've traditionally accepted "name := value" syntax for
cursor arguments in plpgsql. But it turns out that the
equivalent statements in Oracle use "name => value".
Since we accept both forms of punctuation for function
arguments, it makes sense to do the same here.

Author: Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>
Reviewed-by: Gilles Darold <gilles(at)darold(dot)net>
Discussion: https://postgr.es/m/CAFj8pRA3d0ARQEMbABa1n6q25AUdNmyO8aGs56XNf9pD4sRMjQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/246dedc5d028800b393920184e5e6319c6805253

Modified Files
--------------
doc/src/sgml/plpgsql.sgml | 8 +++++---
src/pl/plpgsql/src/pl_gram.y | 13 ++++++++-----
src/test/regress/expected/plpgsql.out | 6 ++++--
src/test/regress/sql/plpgsql.sql | 6 ++++--
4 files changed, 21 insertions(+), 12 deletions(-)