pgsql: Add input function for data type pg_dependencies

Add input function for data type pg_dependencies

pg_dependencies is used as data type for the contents of dependencies
extended statistics. This new input function consumes the format that
has been established by e76defbcf09e for the output function of
pg_dependencies, enforcing some sanity checks for:
- Checks for the input object, which should be a one-dimension array
with correct attributes and values.
- The key names: "attributes", "dependency", "degree". All are
required, other key names are blocked.
- Value types for each key: "attributes" requires an array of integers,
"dependency" an attribute number, "degree" a float.
- List of attributes. In this case, it is possible that some
dependencies are not listed in the statistics data, as items with a
degree of 0 are discarded when building the statistics. This commit
includes checks for simple scenarios, like duplicated attributes, or
overlapping values between the list of "attributes" and the "dependency"
value. Even if the input function considers the input as valid, a value
still needs to be cross-checked with the attributes defined in a
statistics object at import.
- Based on the discussion, the checks on the values are loose, as there
is also an argument for potentially stats injection. For example,
"degree" should be defined in [0.0,1.0], but a check is not enforced.

This is required for a follow-up patch that aims to implement the import
of extended statistics. Some tests are added to check the code paths of
the JSON parser checking the shape of the pg_dependencies inputs, with
91% of code coverage reached. The tests are located in their own new
test file, for clarity.

Author: Corey Huinker <corey(dot)huinker(at)gmail(dot)com>
Reviewed-by: Jian He <jian(dot)universality(at)gmail(dot)com>
Reviewed-by: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Reviewed-by: Michael Paquier <michael(at)paquier(dot)xyz>
Reviewed-by: Yuefei Shi <shiyuefei1004(at)gmail(dot)com>
Discussion: https://postgr.es/m/CADkLM=dpz3KFnqP-dgJ-zvRvtjsa8UZv8wDAQdqho=qN3kX0Zg@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/e1405aa5e3acd55a77838b0b7944198735ffccdf

Modified Files
--------------
src/backend/utils/adt/pg_dependencies.c | 791 +++++++++++++++++++++++++-
src/test/regress/expected/pg_dependencies.out | 540 ++++++++++++++++++
src/test/regress/parallel_schedule | 2 +-
src/test/regress/sql/pg_dependencies.sql | 133 +++++
src/tools/pgindent/typedefs.list | 2 +
5 files changed, 1459 insertions(+), 9 deletions(-)