Doc: Fix various inconsistencies
This fixes multiple areas of the documentation:
- COPY for its past compatibility section.
- SET ROLE mentioning INHERITS instead of INHERIT
- PREPARE referring to stmt_name, that is not present.
- Extension documentation about format name with upgrade scripts.
Backpatch down to 9.4 for the relevant parts.
Author: Alexander Lakhin
Discussion: https://postgr.es/m/
bf95233a-9943-b341-e2ff-
a860c28af481@gmail.com
Backpatch-through: 9.4