pgsql: Fix oversights in pg_event_trigger_dropped_objects() fixes.

Fix oversights in pg_event_trigger_dropped_objects() fixes.

Commit a0b99fc12 caused pg_event_trigger_dropped_objects()
to not fill the object_name field for schemas, which it
should have; and caused it to fill the object_name field
for default values, which it should not have.

In addition, triggers and RLS policies really should behave
the same way as we're making column defaults do; that is,
they should have is_temporary = true if they belong to a
temporary table.

Fix those things, and upgrade event_trigger.sql's woefully
inadequate test coverage of these secondary output columns.

As before, back-patch only to v15.

Reported-by: Sergey Shinderuk <s(dot)shinderuk(at)postgrespro(dot)ru>
Author: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Discussion: https://postgr.es/m/bd7b4651-1c26-4d30-832b-f942fabcb145@postgrespro.ru
Backpatch-through: 15

Branch
------
REL_15_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/33e49ee014b07118bcce5490e3586dc605b2d302

Modified Files
--------------
src/backend/commands/event_trigger.c | 88 ++++++++++++-
src/test/regress/expected/event_trigger.out | 184 +++++++++++++++++-----------
src/test/regress/sql/event_trigger.sql | 55 +++++++--
3 files changed, 243 insertions(+), 84 deletions(-)