[C++] Export arrow_bundled_dependencies by install(TARGETS) instead of creating it in ArrowConfig.cmake #55583

Describe the enhancement requested

arrow_create_merged_static_lib() creates arrow_bundled_dependencies as an IMPORTED library. We can't use install(TARGETS) for it. So we install only the archive by install(FILES) and create Arrow::arrow_bundled_dependencies manually in ArrowConfig.cmake.

So ArrowConfig.cmake needs to do things that CMake usually does for us:

We know everything about the bundled dependencies at build time. We should define arrow_bundled_dependencies as a normal (not IMPORTED) static library target with its dependencies and export it by install(TARGETS ... EXPORT ...). Then we can remove the code that creates Arrow::arrow_bundled_dependencies from ArrowConfig.cmake. Each bundled dependency can declare the libraries it needs where we build it in ThirdpartyToolchain.cmake. We can do the same for arrow_gcs_bundled_dependencies.

Component(s)

C++