pgsql: Implement type regcollation

Implement type regcollation

This will be helpful for a following commit and it's also just
generally useful, like the other reg* types.

Author: Julien Rouhaud
Reviewed-by: Thomas Munro and Michael Paquier
Discussion: /messages/by-id/CAEepm=0uEQCpfq_+LYFBdArCe4Ot98t1aR4eYiYTe=yavQygiQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/a2b1faa0f279f18517adc1dd969e5f026eb51d33

Modified Files
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doc/src/sgml/datatype.sgml | 10 +++
doc/src/sgml/func.sgml | 13 ++-
doc/src/sgml/ref/pgupgrade.sgml | 1 +
src/backend/utils/adt/regproc.c | 152 ++++++++++++++++++++++++++++++++++
src/bin/pg_upgrade/check.c | 1 +
src/include/catalog/catversion.h | 2 +-
src/include/catalog/pg_cast.dat | 14 ++++
src/include/catalog/pg_proc.dat | 15 ++++
src/include/catalog/pg_type.dat | 4 +
src/test/regress/expected/regproc.out | 40 +++++++++
src/test/regress/sql/regproc.sql | 7 ++
11 files changed, 256 insertions(+), 3 deletions(-)