Integrate query IDs with the hint table

The hint table is reworked so as the normalized query string is replaced by the query ID generated by PostgreSQL, based on the jumbling done by the backend. This has multiple advantages:

Less bloat in the hint table, as query strings are replaced by bigint to track the query ID associated with a hint.
Less work for the module. Query normalization consumes cycles to apply the constants to the string for the match in the hint table. This code was copy-pasted from pg_stat_statements, and there is no need for it anymore.
Less error-prone, as a type in the data inserted in the hint table could easily cause a mismatch fail when looking for an entry.

Regression tests are adjusted to cope with this patch, where a PL/PgSQL function is added to be able to retrieve the query ID from a query string, as a wrapper for EXPLAIN (VERBOSE, JSON FORMAT). The query IDs can vary across platforms, so these are hidden to keep the tests portable. The following tweaks are done to the regression tests:

pg_hint_plan.sql has been switched to use this wrapper, with no changes in the regression test coverage.
ut-A, similarly, switches to use the function to retrieve query IDs. A use-case was becoming useless, where we checked for two hints set for the same query ID computed.
ut-T included two tests with CTAS and DECLARE, which interact badly with the PL wrapper. These could be covered with pg_stat_statements, but this dependency is planned to be removed from this test suite, and they covered rather edge cases with limited values with the query ID integration.

The documentation is updated, and the code in charge of the query normalization that was inherited from pg_stat_statements is removed, shaving a good chunk of code. On version upgrade, the past table is removed, replaced by the new one. Using the hint table requires an upgrade up to 1.7.0.

ossc-db / pg_hint_plan

Integrate query IDs with the hint table #193