The canonical config file is in src/backend/gpopt/.clang-format (instead
of under the non-existent src/backend/gporca), I've created one (instead
of two) symlink, for GPOPT headers. Care has been taken to repoint the
symlink to the canonical config under gpopt, instead of gpopt as it is
under HEAD.

This is spiritually a cherry-pick of commit 2f7dd76c.
(cherry picked from commit 2f7dd76c)

The IMemoryPool interface was removed in ORCA to remove an unnecessary
abstraction layer and avoid costly casting.

Corresponding ORCA commit: e64a2b42

Bumps ORCA version to 3.46.0
Authored-by: NChris Hajas <chajas@pivotal.io>

As part of moving away from Hungarian notation in the GPORCA codebase,
the integration points between GPORCA and GPDB in the translator have
been renamed to the new convention used in GPORCA. The libraries
currently updated to the new notation in GPORCA are Naucrates and GPOS.
The new naming convention is a custom version of common C++ naming
conventions. The style guide for this convention can be found in the
GPORCA repository.

Also bump ORCA version to 2.69.0
Co-authored-by: NShreedhar Hardikar <shardikar@pivotal.io>
Co-authored-by: NMelanie Plageman <mplageman@pivotal.io>
Co-authored-by: NEkta Khanna <ekhanna@pivotal.io>
Co-authored-by: NAbhijit Subramanya <asubramanya@pivotal.io>
Co-authored-by: NSambitesh Dash <sdash@pivotal.io&gt;&lt;Paste>
Co-authored-by: NDhanashree Kashid <dkashid@pivotal.io>
Co-authored-by: NOmer Arap <oarap@pivotal.io>

ORCA has historically ignored type modifiers from databases that support
them, noticeably Postgres and Greenplum. This has led to surprises in a
few cases:

1. The output description over the wire (for Postgres protocol) will
lose the type modifier information, which often meant length. This
surprises code that expects a non-default type modifier, e.g. a JDBC
driver.

2. The executor in some cases -- notably DML -- expects a precise type
modifier. Because ORCA always erases the type modifiers and presents a
default, the executor is forced to find that information elsewhere.

After this commit, ORCA will be aware of type modifiers in table
columns, scalar identifiers, constants, and length-coercion casts.
Signed-off-by: NShreedhar Hardikar <shardikar@pivotal.io>
(cherry picked from commit 2d907526)

This allows removing all the code in CTranslatorDXLToPlStmt that tracked
the parent of each call.

I found the plan node IDs awkward, when I was hacking on
CTranslatorDXLToPlStmt. I tried to make a change where a function would
construct a child Plan node first, and a Result node on top of that, but
only if necessary, depending on the kind of child plan. The parent plan
node IDs made it impossible to construct a part of Plan tree like that, in
a bottom-up fashion, because you always had to pass the parent's ID when
constructing a child node. Now that is possible.

It gives compiler warnings:

/home/heikki/gpdb/orca-install/include/gpos/common/CDynamicPtrArray.inl:382:3: warning: nonnull argument ‘this’ compared to NULL [-Wnonnull-compare]
   if (NULL == this)
   ^~

Long time ago, a hack was put in place in GPDB to use the "scan" slot,
instead of the "outer" slot which is used in the upstream, to hold the
result of an Agg or Window plan node's child. It's not clear to me why
that was done. There was even a comment in fix_upper_expr() saying we
wouldn't need it if we just fixed the executor to not contain that hack,
and there was also a TODO comment in CMappingColIdVarPlStmt.cpp about
that.

Everything seems to work without those hacks, so revert this thing back
to the way it works in the upstream. This is simpler in its own right,
and also reduces our diff vs. upstream, which will make merging easier
in the future.