pgsql: Add common interface for TBMIterators

Add common interface for TBMIterators

Add and use TBMPrivateIterator, which replaces the current TBMIterator
for serial use cases, and repurpose TBMIterator to be a unified
interface for both the serial ("private") and parallel ("shared") TID
Bitmap iterator interfaces. This encapsulation simplifies call sites for
callers supporting both parallel and serial TID Bitmap access.
TBMIterator is not yet used in this commit.

Author: Melanie Plageman
Reviewed-by: Tomas Vondra, Heikki Linnakangas
Discussion: https://postgr.es/m/063e4eb4-32d9-439e-a0b1-75565a9835a8%40iki.fi

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/7f9d4187e7bab10329cc00aff34cfba08248d4be

Modified Files
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src/backend/access/gin/ginget.c           |  10 +--
src/backend/access/gin/ginscan.c          |   2 +-
src/backend/access/heap/heapam_handler.c  |   2 +-
src/backend/executor/nodeBitmapHeapscan.c |  25 +++----
src/backend/nodes/tidbitmap.c             | 114 +++++++++++++++++++++++-------
src/include/access/gin_private.h          |   2 +-
src/include/access/relscan.h              |   4 +-
src/include/nodes/execnodes.h             |   2 +-
src/include/nodes/tidbitmap.h             |  30 ++++++--
src/tools/pgindent/typedefs.list          |   1 +
10 files changed, 140 insertions(+), 52 deletions(-)