GH-47576: [C++][Acero] Fix C++23 build

[jmcarcell]

Rationale for this change

Related to #47576.

In C++23, Clang diagnoses the conversion from AsofJoinNode* to ExecNode*
while instantiating std::make_unique<BackpressureController>. At the current
definition site, AsofJoinNode is still incomplete, causing the Acero build to
fail.

What changes are included in this PR?

Declare InputState::Make in InputState and define it after AsofJoinNode is
complete. This makes the derived-to-base conversion valid without changing runtime
behavior.

AI assistance: Codex drafted and evaluated this source-ordering change. The
automated checks below were run before opening the PR.

Are these changes tested?

• cmake --build cpp/build-clang22-cxx23-release --target arrow_acero_static --parallel 2
  (Clang 22.1.8, Release, C++23)
• ctest -j 16 --output-on-failure in
  cpp/build-clang22-cxx23-release-tests/src/arrow/acero: 14/14 tests passed
• clang-format --dry-run --Werror cpp/src/arrow/acero/asof_join_node.cc
• git diff --check

Original `Clang 22` `C++23` diagnostic

In file included from /arrow/src/arrow/acero/asof_join_node.cc:18:
In file included from /arrow/src/arrow/acero/asof_join_node.h:20:
In file included from /arrow/src/arrow/acero/options.h:21:
In file included from /usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/16/../../../../include/c++/16/memory:80:
/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/16/../../../../include/c++/16/bits/unique_ptr.h:1105:34: error: no matching constructor for initialization of 'arrow::acero::BackpressureController'
 1105 |     { return unique_ptr<_Tp>(new _Tp(std::forward<_Args>(__args)...)); }
      |                                  ^   ~~~~~~~~~~~~~~~~~~~~~~~~~~~
/arrow/src/arrow/acero/asof_join_node.cc:515:14: note: in instantiation of function template specialization 'std::make_unique<arrow::acero::BackpressureController, arrow::acero::ExecNode *&, arrow::acero::AsofJoinNode *&, std::atomic<int> &>' requested here
  515 |         std::make_unique<BackpressureController>(
      |              ^
/arrow/src/arrow/acero/asof_join_node.cc:464:3: note: candidate constructor not viable: cannot convert argument of incomplete type 'arrow::acero::AsofJoinNode *' to 'ExecNode *' for 2nd argument
  464 |   BackpressureController(ExecNode* node, ExecNode* output,
      |   ^                                      ~~~~~~~~~~~~~~~~
/arrow/src/arrow/acero/asof_join_node.cc:462:7: note: candidate constructor (the implicit copy constructor) not viable: requires 1 argument, but 3 were provided
  462 | class BackpressureController : public BackpressureControl {
      |       ^~~~~~~~~~~~~~~~~~~~~~
/arrow/src/arrow/acero/asof_join_node.cc:462:7: note: candidate constructor (the implicit move constructor) not viable: requires 1 argument, but 3 were provided
  462 | class BackpressureController : public BackpressureControl {
      |       ^~~~~~~~~~~~~~~~~~~~~~
/arrow/src/arrow/acero/asof_join_node.cc:794:17: warning: private field 'node_' is not used [-Wunused-private-field]
  794 |   AsofJoinNode* node_;
      |                 ^
/arrow/src/arrow/acero/asof_join_node.cc:796:10: warning: private field 'index_' is not used [-Wunused-private-field]
  796 |   size_t index_;
      |          ^
2 warnings and 1 error generated.

Are there any user-facing changes?

No public API changes. This restores the ability to compile the Acero component
with the affected Clang 22/C++23 configuration.

• GitHub Issue: [C++][Acero] Build failure on OS X and cppstd 23 #47576

[Copilot]

Pull request overview

Adjusts function definition ordering in Acero’s AsofJoinNode implementation to satisfy stricter C++23 type-completeness requirements when constructing backpressure control (resolving a C++23 build failure referenced by GH-47207).

Changes:

• Moves InputState::Make from an in-class definition to an out-of-line definition placed after AsofJoinNode is fully defined.
• Preserves existing backpressure controller/handler setup logic while enabling C++23 to perform the AsofJoinNode* → ExecNode* conversion during BackpressureController construction.

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[github-actions]

⚠️ GitHub issue #47576 has been automatically assigned in GitHub to PR creator.

[github-actions]

⚠️ GitHub issue #47576 has been automatically assigned in GitHub to PR creator.

[github-actions]

⚠️ GitHub issue #47576 has been automatically assigned in GitHub to PR creator.

[jmcarcell]

The build error seems unrelated, with lots of HTTP errors. And the pre-commit one I don't understand it, also seems unrelated and I'm not changing any python code.