GH-48091: [C++] Use FetchContent for bundled c-ares

[raulcd]

Do not merge

This PR is implemented on top of:

• GH-48074: [C++] Use FetchContent for bundled Abseil #48075

Rationale for this change

As a follow up of requiring a minimum CMake version >= 3.25 we discussed moving our dependencies from ExternalProject to FetchContent. This can heavily simplify our third party dependency management. Moving c-ares is the next step before moving grpc.

What changes are included in this PR?

The general change is moving from ExternalProject to FetchContent.

It also add some required integration due to other dependencies, like grpc, using ExternalProject. We not only have to build but also install in order for those other dependencies to find c-ares. This causes some timing issues between config, build, install that requires us to create a custom target to depend on so the other dependencies find abseil.

Are these changes tested?

Yes, the changes are tested locally and on CI.

Are there any user-facing changes?

No

• GitHub Issue: [C++] Use FetchContent for bundled c-ares #48091

[raulcd]

@github-actions crossbow submit bundled

[github-actions]

Revision: 7e7f084

Submitted crossbow builds: ursacomputing/crossbow @ actions-d7ad44f8f1

Task	Status
test-r-depsource-bundled
test-ubuntu-22.04-cpp-bundled
test-ubuntu-24.04-cpp-bundled-offline
test-ubuntu-24.04-cpp-gcc-13-bundled