pgsql: pg_freespacemap: Use SQL-standard function bodies

pg_freespacemap: Use SQL-standard function bodies

72a5b1fc8804 was the piece missing for the conversion of this module.
pg_freespace is bumped to 1.3, with its function pg_freespace(regclass)
converted to this new style.

There are other modules in the tree that need a similar treatment; these
will be handled later.

Author: Tom Lane
Reviewed-by: Ronan Dunklau
Discussion: /messages/by-id/3395418.1618352794@sss.pgh.pa.us

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/3f323eba89fb1ea2220cfe48ea7d9529fffe5cb6

Modified Files
--------------
contrib/pg_freespacemap/Makefile | 4 +++-
contrib/pg_freespacemap/meson.build | 1 +
contrib/pg_freespacemap/pg_freespacemap--1.2--1.3.sql | 13 +++++++++++++
contrib/pg_freespacemap/pg_freespacemap.control | 2 +-
4 files changed, 18 insertions(+), 2 deletions(-)