pgsql: Fix connection handling for DEALLOCATE and DESCRIBE statements

Fix connection handling for DEALLOCATE and DESCRIBE statements

After binding a statement to a connection with DECLARE STATEMENT the connection
was still not used for DEALLOCATE and DESCRIBE statements. This patch fixes
that, adds a missing warning and cleans up the code.

Author: Hayato Kuroda
Reviewed-by: Kyotaro Horiguchi, Michael Paquier
Discussion: https://postgr.es/m/TYAPR01MB5866BA57688DF2770E2F95C6F5069%40TYAPR01MB5866.jpnprd01.prod.outlook.com

Branch
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REL_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/a945f5527322d18d02990a9772a893f741e7d8df

Modified Files
--------------
src/interfaces/ecpg/preproc/descriptor.c | 16 ++-
src/interfaces/ecpg/preproc/ecpg.addons | 8 +-
src/interfaces/ecpg/preproc/ecpg.header | 12 +-
src/interfaces/ecpg/preproc/ecpg.trailer | 44 +++----
src/interfaces/ecpg/preproc/ecpg.type | 3 +-
src/interfaces/ecpg/preproc/output.c | 9 --
src/interfaces/ecpg/preproc/type.h | 6 +
src/interfaces/ecpg/test/expected/sql-declare.c | 137 ++++++++++++++++++---
.../ecpg/test/expected/sql-declare.stderr | 56 ++++++---
.../ecpg/test/expected/sql-declare.stdout | 2 +
src/interfaces/ecpg/test/sql/declare.pgc | 40 +++++-
11 files changed, 258 insertions(+), 75 deletions(-)