[C++] Refactor bundled dependencies from ExternalProject to FetchContent

[amoeba]

Describe the enhancement requested

This is a tracking issue for refactoring the bundled part of the Arrow C++ build from using CMake ExternalProject to FetchContent. Please comment on this issue if you have anything to add to this post or want to help clarify anything.

Related issues:

• The build system is currently being upgraded from 3.16 to 3.25: GH-44950: [C++] Bump minimum CMake version to 3.25 #44989

Related discussions:

• Zulip: Dev > CMake minimum required version (2024/11/12)

Tasks that depend on FetchContent:

• [Release][Packaging] Address notes in vcpkg x64-windows-static build #45297
  • Once we use FetchContent, the patch described in this issue can be removed from our vcpkg port
• [C++] Update bundled AWS SDK for C++ from 1.10.55 #45195
• [C++] Update bundled Abseil and gRPC #45063
• [C++] Use FetchContent for bundled Abseil #48074
• [C++] Use FetchContent for bundled c-ares #48091
• [C++] Use FetchContent for bundled RE2 #48178
• [C++] Use FetchContent for bundled Protobuf #48181
• [C++] Use FetchContent for bundled gRPC #48248
• [C++] Use FetchContent for bundled CRC32C #48315
• [C++] Use FetchContent for bundled nlohmann-json #48316
• [C++] Use FetchContent for bundled google-cloud-cpp #48317
• [C++] Use FetchContent for bundled opentelemetry #48555

cc @kou @assignUser @raulcd

Component(s)

C++

[assignUser]

Thanks, this is a big chunk of work but it will make following version bumps much smoother and make a bunch of workarounds superfluous.

Design wise a main point we should follow is to use sub dirs for all dependencies to avoid dir level variables leaking into the main build.