ARROW-13534: [C++] Improve csv chunker
ARROW-13534: [C++] Improve csv chunker

Add hints to help compiler deleting dead code per template augments.
Tested with clang-10, gcc-9.3, on x86 and Arm, observed ~20% uplift for
quoting=false benchmark. Probably due to better code locality.

Closes #10859 from cyb70289/13534-csv-chunker

Authored-by: Yibo Cai <e732a3f0de35687e82bda0008a72e443d2f69704@arm.com>
Signed-off-by: Antoine Pitrou <9359a4d812173b65a3a0094cd86363e79731a3c2@python.org>

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