PG16 compatibility - Part 2
Part 1 provided successful compilation against pg16beta2.
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This PR provides ruleutils changes with pg16beta2 and successful CREATE EXTENSION command.
Note that more changes are needed in order to have successful regression tests.
More commits are coming soon ...
For any_value changes, I referred to this commit
8ef94dc1f5
where we did something similar for PG14 support.