Streamify more code paths

Hi Hackers,

I noticed several additional paths in contrib modules, beyond [1],
that are potentially suitable for streamification:

1) pgstattuple — pgstatapprox.c and parts of pgstattuple_approx_internal
2) Bloom — scan paths in blgetbitmap() and maintenance paths in blbulkdelete()

The following patches streamify those code paths. No benchmarks have
been run yet.

[1] https://www.postgresql.org/message-id/flat/CABPTF7UeN2o-trr9r7K76rZExnO2M4SLfvTfbUY2CwQjCekgnQ%40mail.gmail.com

Feedbacks welcome.

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Best,
Xuneng