pgsql: Test additional speculative conflict scenarios.

Test additional speculative conflict scenarios.

Previously, the speculative insert tests did not cover the case when a
tuple t is inserted into a table with a unique index on a column but
before it can insert into the index, a concurrent transaction has
inserted a conflicting value into the index and the insertion of tuple t
must be aborted.

The basic permutation is one session successfully inserts into the table
and an associated unique index while a concurrent session successfully
inserts into the table but discovers a conflict before inserting into
the index and must abort the insertion.

Several variants on this include:
- swap which session is successful
- first session insert transaction does not commit, so second session
must wait on a transaction lock
- first session insert does not "complete", so second session must wait
on a speculative insertion lock

Also, refactor the existing TOAST table upsert test to be in the same
spec and reuse the steps.

Author: Melanie Plageman, Ashwin Agrawal, Andres Freund
Reviewed-by: Andres Freund, Taylor Vesely
Discussion: https://postgr.es/m/CAAKRu_ZRmxy_OEryfY3G8Zp01ouhgw59_-_Cm8n7LzRH5BAvng@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/43e08419708a938236e76cd50de2db512e1c3a0c

Modified Files
--------------
.../expected/insert-conflict-specconflict.out      | 277 +++++++++++++++++----
.../isolation/expected/insert-conflict-toast.out   |  15 --
src/test/isolation/isolation_schedule              |   1 -
.../specs/insert-conflict-specconflict.spec        | 140 +++++++++--
.../isolation/specs/insert-conflict-toast.spec     |  51 ----
5 files changed, 356 insertions(+), 128 deletions(-)