apacheGH-38381: [C++][Acero] Create a sorted merge node (apache#38380)

### Rationale for this change

This is an implementation of a node that can merge N sorted inputs (only in ascending order for a first pass).

Where possible I have shared components with `asof_join_node.cc`.

Full description/use case is described in apache#38381

### What changes are included in this PR?

* Take out relevant guts of asofjoin to stream data top to bottom/consume in a non blocking manner
* Implement a sorted merger

### Are these changes tested?

Basic test added. Locally I have tested this on 100+ gigabytes of parquet, sharded across 50+ files. Happy to add a benchmark test on top of the basic test, but submitting now for code feedback.

### Are there any user-facing changes?

Yes, `sorted_merge` is now an exposed declaration

Lead-authored-by: Jeremy Aguilon <[email protected]>
Co-authored-by: jeremy <[email protected]>
Co-authored-by: Weston Pace <[email protected]>
Signed-off-by: Weston Pace <[email protected]>

cpp/src/arrow/acero/CMakeLists.txt

@@ -49,9 +49,11 @@ set(ARROW_ACERO_SRCS
     project_node.cc
     query_context.cc
     sink_node.cc
+    sorted_merge_node.cc
     source_node.cc
     swiss_join.cc
     task_util.cc
+    time_series_util.cc
     tpch_node.cc
     union_node.cc
     util.cc)
@@ -173,11 +175,13 @@ add_arrow_acero_test(hash_join_node_test SOURCES hash_join_node_test.cc
 add_arrow_acero_test(pivot_longer_node_test SOURCES pivot_longer_node_test.cc
                      test_nodes.cc)
 
-# asof_join_node uses std::thread internally
+# asof_join_node and sorted_merge_node use std::thread internally
 # and doesn't use ThreadPool so it will
 # be broken if threading is turned off
 if(ARROW_ENABLE_THREADING)
   add_arrow_acero_test(asof_join_node_test SOURCES asof_join_node_test.cc test_nodes.cc)
+  add_arrow_acero_test(sorted_merge_node_test SOURCES sorted_merge_node_test.cc
+                       test_nodes.cc)
 endif()
 
 add_arrow_acero_test(tpch_node_test SOURCES tpch_node_test.cc)