pgsql: Cleanup covering infrastructure

Cleanup covering infrastructure

- Explicitly forbids opclass, collation and indoptions (like DESC/ASC etc) for
including columns. Throw an error if user points that.
- Truncated storage arrays for such attributes to store only key atrributes,
added assertion checks.
- Do not check opfamily and collation for including columns in
CompareIndexInfo()

Discussion: https://www.postgresql.org/message-id/5ee72852-3c4e-ee35-e2ed-c1d053d45c08@sigaev.ru

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/c266ed31a8a3beed3533e6a78faeca78234cbd43

Modified Files
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src/backend/catalog/index.c | 22 ++++++++++++++----
src/backend/commands/indexcmds.c | 44 +++++++++++++++++++++++++----------
src/backend/optimizer/path/indxpath.c | 40 +++++++++++++++++++++++--------
src/backend/optimizer/util/plancat.c | 4 ++--
src/backend/parser/parse_utilcmd.c | 3 ---
src/backend/utils/adt/ruleutils.c | 6 ++---
src/backend/utils/adt/selfuncs.c | 2 ++
src/backend/utils/cache/relcache.c | 8 +++----
8 files changed, 90 insertions(+), 39 deletions(-)