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ARROW-15248: [C++][Docs] Improve docs about linting/formatting

This improves the docs by clarifying a few things:

* How to lint/format using a CMake build,
* The linter/formatter version must match exactly,
* Formatting can be done by commenting on a PR.

Also, the example Archery command is extended to list all the C++ formatters, and we describe where to get a copy of the LLVM tools.

Closes #12085 from lidavidm/arrow-15248

Authored-by: David Li <li.davidm96@gmail.com>
Signed-off-by: Antoine Pitrou <antoine@python.org>