pgsql: Refactor ChangeVarNodesExtended() using the custom callback

Refactor ChangeVarNodesExtended() using the custom callback

fc069a3a6319 implemented Self-Join Elimination (SJE) and put related logic
to ChangeVarNodes_walker(). This commit provides refactoring to remove the
SJE-related logic from ChangeVarNodes_walker() but adds a custom callback to
ChangeVarNodesExtended(), which has a chance to process a node before
ChangeVarNodes_walker(). Passing this callback to ChangeVarNodesExtended()
allows SJE-related node handling to be kept within the analyzejoins.c.

Reported-by: Richard Guo <guofenglinux(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAMbWs49PE3CvnV8vrQ0Dr%3DHqgZZmX0tdNbzVNJxqc8yg-8kDQQ%40mail.gmail.com
Author: Andrei Lepikhov <lepihov(at)gmail(dot)com>
Author: Alexander Korotkov <aekorotkov(at)gmail(dot)com>

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/250a718aadad68793e82103282247556a46a3cfc

Modified Files
--------------
src/backend/optimizer/plan/analyzejoins.c | 160 +++++++++++++++++++++++++++---
src/backend/rewrite/rewriteManip.c | 138 ++++++--------------------
src/include/rewrite/rewriteManip.h | 17 +++-
src/tools/pgindent/typedefs.list | 1 +
4 files changed, 192 insertions(+), 124 deletions(-)