pgsql: Add regression tests for REPLICA IDENTITY with dropped indexes

Add regression tests for REPLICA IDENTITY with dropped indexes

REPLICA IDENTITY USING INDEX behaves the same way as NOTHING if the
associated index is dropped, even if there is a primary key that could
be used as a fallback for the changes generated. There have never been
any tests to cover such scenarios, so this commit closes the gap.

Author: Michael Paquier
Reviewed-by: Masahiko Sawada, Rahila Syed, Euler Taveira
Discussion: /messages/by-id/20200522035028.GO2355@paquier.xyz

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/fe7fd4e9613f58262d30782a34b01cc0c4cbbeb5

Modified Files
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contrib/test_decoding/expected/ddl.out | 71 +++++++++++++++++++++++++++++++++-
contrib/test_decoding/sql/ddl.sql | 31 +++++++++++++++
2 files changed, 101 insertions(+), 1 deletion(-)