pgsql: bufmgr: Separate keys for private refcount infrastructure

bufmgr: Separate keys for private refcount infrastructure

This makes lookups faster, due to allowing auto-vectorized lookups. It is also
beneficial for an upcoming patch, independent of auto-vectorization, as the
upcoming patch wants to track more information for each pinned buffer, making
the existing loop, iterating over an array of PrivateRefCountEntry, more
expensive due to increasing its size.

Reviewed-by: Melanie Plageman <melanieplageman(at)gmail(dot)com>
Discussion: https://postgr.es/m/fvfmkr5kk4nyex56ejgxj3uzi63isfxovp2biecb4bspbjrze7@az2pljabhnff

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/edbaaea0a95ef1c32ffe8aa62e1556588c7a714b

Modified Files
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src/backend/storage/buffer/bufmgr.c | 141 ++++++++++++++++++++++++------------
src/tools/pgindent/typedefs.list | 1 +
2 files changed, 97 insertions(+), 45 deletions(-)