[C++] FindBrotliAlt.cmake and Findutf8proc.cmake use ARROW_VCPKG

[kou]

Describe the bug, including details regarding any error messages, version, and platform.

#46467 changed FindBrotliAlt.cmake and Findutf8proc.cmake to use ARROW_VCPKG instead of ARROW_PACKAGE_KIND. It works in Apache Arrow C++ build but doesn't work when users use find_package(Arrow) because ARROW_VCPKG isn't exported in ArrowConfig.cmake.

See also: apache/arrow-java#764

Component(s)

C++

[kou]

Issue resolved by pull request 46565
#46565