pgsql: Improve parsing of options of CREATE/ALTER SUBSCRIPTION

Improve parsing of options of CREATE/ALTER SUBSCRIPTION

This simplifies the code so as it is not necessary anymore for the
caller of parse_subscription_options() to zero SubOpts, holding a
bitmaps of the provided options as well as the default/parsed option
values.  This also simplifies some checks related to the options
supported by a command when checking for incompatibilities.

While on it, the errors generated for unsupported combinations with
"slot_name = NONE" are reordered.  This may generate a different errors
compared to the previous major versions, but users have to go through
all those errors to get a correct command in this case when using
incorrect values for options "enabled" and "create\slot", so at the end
the resulting command would remain the same.

Author: Peter Smith
Reviewed-by: Nathan Bossart
Discussion: https://postgr.es/m/CAHut+PtXHfLgLHDDJ8ZN5f5Be_37mJoxpEsRg8LNmm4XCr06Rw@mail.gmail.com

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/00029deaf65aad47044d9290fe80f2f68601f7ac

Modified Files
--------------
src/backend/commands/subscriptioncmds.c    | 73 ++++++++++++++----------------
src/test/regress/expected/subscription.out |  2 +-
src/test/regress/sql/subscription.sql      |  2 +-
3 files changed, 35 insertions(+), 42 deletions(-)