System columns not returned by certain table AM APIs

[soumyadeep2007]

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This leads to garbage values for xmin and cmin and an ERROR for xmax and cmax.

This is not an exhaustive list of operations for which we see this behavior:

1. INSERT/UPDATE/DELETE..RETURNING <tx_column>,...
2. SELECT <tx_column>,.. FROM ..;

Discussion: https://www.postgresql.org/message-id/CAE-ML%2B_mHwV7EpVX6WoVUedVCMOaRM_4rO_%2BDO86mSNxAVo5%2BQ%40mail.gmail.com