Misc Fixes for Prisma

[NathanGabrielson]

3 things in this PR:

1. Makes version numbers consistent. I used 15.17 which is the latest version of postgresql 15.
2. Make the col_description, obj_description, and shobj_description return the correct value for "no comments", rather than "empty comments". They are still no-op functions but now return NULL instead of empty strings. More detailed information on these functions can be found here
3. generate_subscripts is a set returning function that returns the indices of the array you give it. So for instance the array [10, 40, 23] will return {1, 2, 3}. Most postgresql array types are 1-indexed, except for the types oidvector and int2vector. I added a fix so that generate_subscripts respects those two's unique indexing. More on generate_subscripts here. oidvector and int2vector don't seem to have standard docs pages but this site provides basic details.

[github-actions]

	Main	PR
covering_index_scan_postgres	579.72/s	574.84/s	-0.9%
index_join_postgres	123.45/s	123.09/s	-0.3%
index_join_scan_postgres	182.19/s	181.05/s	-0.7%
index_scan_postgres	10.97/s	11.03/s	+0.5%
oltp_point_select	2363.73/s	2349.48/s	-0.7%
oltp_read_only	1686.14/s	1680.51/s	-0.4%
select_random_points	110.02/s	111.40/s	+1.2%
select_random_ranges	445.41/s	438.13/s	-1.7%
table_scan_postgres	10.83/s	10.82/s	-0.1%
types_table_scan_postgres	4.94/s	4.97/s	+0.6%

[github-actions]

	Main	PR
Total	42090	42090
Successful	17765	17765
Failures	24325	24325
Partial Successes1	5573	5573

	Main	PR
Successful	42.2072%	42.2072%
Failures	57.7928%	57.7928%

Footnotes

1. These are tests that we're marking as Successful, however they do not match the expected output in some way. This is due to small differences, such as different wording on the error messages, or the column names being incorrect while the data itself is correct. ↩

[fulghum]

Looks good!