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ARROW-15550: [C++] Add optional debug memory checks

Debug memory checks can be enabled by setting the environment variable ARROW_DEBUG_MEMORY_POOL
to one of the recognized values "abort", "trap" or "warn" (regardless of whether Arrow
was compiled in debug or release mode).

The only implemented check adds a suffix past the allocation and checks that it isn't clobbered on deallocation.
Adding a prefix would be more expensive because of alignment constraints.

Also add a fix by Will Jones for ARROW-14047 (Parquet Arrow reader sets null values in buffer overflow), since otherwise CI would fail.

Closes #12330 from pitrou/ARROW-15550-debug-memory-checks

Authored-by: Antoine Pitrou <antoine@python.org>
Signed-off-by: Antoine Pitrou <antoine@python.org>