pgsql: Refactor LogicalTapeSet/LogicalTape interface.

Refactor LogicalTapeSet/LogicalTape interface.

All the tape functions, like LogicalTapeRead and LogicalTapeWrite, now
take a LogicalTape as argument, instead of LogicalTapeSet+tape number.
You can create any number of LogicalTapes in a single LogicalTapeSet, and
you don't need to decide the number upfront, when you create the tape set.

This makes the tape management in hash agg spilling in nodeAgg.c simpler.

Discussion: https://www.postgresql.org/message-id/420a0ec7-602c-d406-1e75-1ef7ddc58d83%40iki.fi
Reviewed-by: Peter Geoghegan, Zhihong Yu, John Naylor

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/c4649cce39a41b27db874e75ddd47adaec1b0ea4

Modified Files
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src/backend/executor/nodeAgg.c | 187 ++++-----------
src/backend/utils/sort/logtape.c | 456 +++++++++++++++----------------------
src/backend/utils/sort/tuplesort.c | 229 +++++++++----------
src/include/nodes/execnodes.h | 3 +-
src/include/utils/logtape.h | 37 ++-
5 files changed, 359 insertions(+), 553 deletions(-)