Allow explicit casting between bytea and uuid.

Allow explicit casting between bytea and uuid.

This enables the use of functions such as encode() and decode() with
UUID values, allowing them to be converted to and from alternative
formats like base64 or hex.

The cast maps the 16-byte internal representation of a UUID directly
to a bytea datum. This is more efficient than going through a text
forepresentation.

Bump catalog version.

Author:	Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>
Co-authored-by: Aleksander Alekseev <aleksander@tigerdata.com>
Reviewed-by: Masahiko Sawada <sawada.mshk@gmail.com>
Reviewed-by: Andrey Borodin <x4mmm@yandex-team.ru>
Reviewed-by: Jelte Fennema-Nio <postgres@jeltef.nl>
Discussion: https://postgr.es/m/CAJ7c6TOramr1UTLcyB128LWMqita1Y7%3Darq3KHaU%3Dqikf5yKOQ%40mail.gmail.com