pgsql: tests: Expand temp table tests to some pin related matters

tests: Expand temp table tests to some pin related matters

Added tests:
- recovery from running out of unpinned local buffers
- that we don't run out of unpinned buffers due to read stream (only recently
fixed, in 92fc6856cb4)
- temp tables can't be dropped while in use by cursors

Discussion: weskknhckugbdm2yt7sa2uq53xlsax67gcdkac34sanb7qpd3p@hcc2wadao5wy
Discussion: /messages/by-id/ge6nsuddurhpmll3xj22vucvqwp4agqz6ndtcf2mhyeydzarst@l75dman5x53p

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/1a22a8a0f1319e3d80cab0962374f235359b59ff

Modified Files
--------------
src/test/regress/expected/temp.out | 156 +++++++++++++++++++++++++++++++++++++
src/test/regress/parallel_schedule | 2 +-
src/test/regress/sql/temp.sql | 107 +++++++++++++++++++++++++
3 files changed, 264 insertions(+), 1 deletion(-)