pgsql: Fix slot type issue for fuzzy distance index scan overout-of-co

Fix slot type issue for fuzzy distance index scan over out-of-core table AM.

For amcanreorderby scans the nodeIndexscan.c's reorder queue holds
heap tuples, but the underlying table likely does not. Before this fix
we'd return different types of slots, depending on whether the tuple
came from the reorder queue, or from the index + table.

While that could be fixed by signalling that the node doesn't return a
fixed type of slot, it seems better to instead remove the separate
slot for the reorder queue, and use ExecForceStoreHeapTuple() to store
tuples from the queue. It's not particularly common to need
reordering, after all.

This reverts most of the iss_ReorderQueueSlot related changes to
nodeIndexscan.c made in 1a0586de3657cd3, except that now
ExecForceStoreHeapTuple() is used instead of ExecStoreHeapTuple().

Noticed when testing zheap against the in-core version of tableam.

Author: Andres Freund

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/b8b94ea129ffc988c2d30eb2b5aa65a93329b8fa

Modified Files
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src/backend/executor/nodeIndexscan.c | 20 ++++++--------------
src/include/nodes/execnodes.h        |  1 -
2 files changed, 6 insertions(+), 15 deletions(-)