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ARROW-10896: [C++][CMake] Rename internal RE2 package name to "re2" from "RE2"

Because upstream uses "re2". If we don't use different package name
such as "RE2", RE2 package is conflicted with other package that uses
RE2 such as gRPC.

This change also includes resolve_dependency() cleanup. There were
some custom resolve_dependency() like codes for packages that need our
custom "Alt" version such as Boost and gRPC. We can use
resolved_dependency() for these packages with the new HAVE_ALT option.

This change also renamed our Boost dependency name to "Boost" from
"BOOST". It means that users need to use -DBoost_SOURCE not
-DBOOST_SOURCE. To keep backward compatibility, -DBOOST_SOURCE is
still accepted when -DBoost_SOURCE isn't specified.

Users also need to use -Dre2_SOURCE not -DRE2_SOURCE. To keep backward
compatibility, -DRE2_SOURCE is still accepted when -Dre2_SOURCE isn't
specified.

Closes #8908 from kou/cpp-re2

Authored-by: Sutou Kouhei <kou@clear-code.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>