PG17 compatibility: Resolve compilation issues

[naisila]

PG17 compatibility - Part 1

This PR provides successful compilation against PG17Beta2.

Notes to reviewer:

• Review commit by commit - it's much cleaner that way.
• When merged, Enable configure and add pg17 build test commits will be reverted. They are part of the PR to make sure that the PG17 build is actually successful - see Build for PG17 in the PR checks. These changes will be merged to the main branch later, when the PG17 support is fully added.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 97.00240% with 25 lines in your changes missing coverage. Please review.

Project coverage is 89.69%. Comparing base (2a263fe) to head (76f60a7). Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7651      +/-   ##
==========================================
- Coverage   89.70%   89.69%   -0.01%     
==========================================
  Files         283      283              
  Lines       60507    60512       +5     
  Branches     7539     7539              
==========================================
  Hits        54275    54275              
- Misses       4076     4080       +4     
- Partials     2156     2157       +1