GH-45034: [C++] Remove Parquet requirement from Arrow Acero and from …

…Arrow Dataset when not necessary (#45035)

### Rationale for this change

Currently we are defining Parquet as a requirement for Acero and for Dataset on `ArrowAceroConfig.cmake.in` and `ArrowDatasetConfig.cmake.in` respectively.

Parquet should never be necessary for Acero and could be necessary for Dataset only if it has been built with Parquet support.

### What changes are included in this PR?

Remove Parquet from `ArrowAceroConfig.cmake.in` and add it as optional dependency for `ArrowDatasetConfig.cmake.in`

### Are these changes tested?

I've tested with a really minimal build of Arrow and Pyarrow. I don't think we want to add a build without Parquet but with Dataset and/or Acero at CI just to test this scenario.
Logs for the local build without Parquet:
```
-- Found Cython version: 3.0.11
-- Arrow version: 19.0.0
-- Found the Arrow shared library: /home/raulcd/code/dist/lib/libarrow.so.1900.0.0
-- Found the Arrow import library: ARROW_IMPORT_LIB-NOTFOUND
-- Found the Arrow static library: 
-- Building PyArrow with Dataset
-- ArrowAcero version: 19.0.0
-- Found the ArrowAcero shared library: /home/raulcd/code/dist/lib/libarrow_acero.so.1900.0.0
-- Found the ArrowAcero import library: ARROW_ACERO_IMPORT_LIB-NOTFOUND
-- Found the ArrowAcero static library: 
-- ArrowDataset version: 19.0.0
-- Found the ArrowDataset shared library: /home/raulcd/code/dist/lib/libarrow_dataset.so.1900.0.0
-- Found the ArrowDataset import library: ARROW_DATASET_IMPORT_LIB-NOTFOUND
-- Found the ArrowDataset static library: 
-- Building PyArrow with Acero
-- Parquet Encryption is NOT Enabled
```

The `IMPORT_LIB-NOTFOUND` has always been present and it's not new.

### Are there any user-facing changes?

No as this should have already been the case.
* GitHub Issue: #45034

Authored-by: Raúl Cumplido <[email protected]>
Signed-off-by: Sutou Kouhei <[email protected]>

cpp/src/arrow/acero/ArrowAceroConfig.cmake.in

@@ -28,7 +28,6 @@
 
 include(CMakeFindDependencyMacro)
 find_dependency(Arrow)
-find_dependency(Parquet)
 
 include("${CMAKE_CURRENT_LIST_DIR}/ArrowAceroTargets.cmake")
 

cpp/src/arrow/dataset/ArrowDatasetConfig.cmake.in

@@ -26,10 +26,12 @@
 
 @PACKAGE_INIT@
 
+set(ARROW_DATASET_REQUIRED_DEPENDENCIES "@ARROW_DATASET_REQUIRED_DEPENDENCIES@")
+
 include(CMakeFindDependencyMacro)
-find_dependency(Arrow)
-find_dependency(ArrowAcero)
-find_dependency(Parquet)
+foreach(dependency ${ARROW_DATASET_REQUIRED_DEPENDENCIES})
+  find_dependency(${dependency})
+endforeach()
 
 include("${CMAKE_CURRENT_LIST_DIR}/ArrowDatasetTargets.cmake")
 

cpp/src/arrow/dataset/CMakeLists.txt

@@ -32,8 +32,10 @@ set(ARROW_DATASET_SRCS
     scan_node.cc)
 
 set(ARROW_DATASET_PKG_CONFIG_REQUIRES "arrow-acero")
+set(ARROW_DATASET_REQUIRED_DEPENDENCIES Arrow ArrowAcero)
 if(ARROW_PARQUET)
   string(APPEND ARROW_DATASET_PKG_CONFIG_REQUIRES " parquet")
+  list(APPEND ARROW_DATASET_REQUIRED_DEPENDENCIES Parquet)
 endif()
 
 set(ARROW_DATASET_STATIC_LINK_LIBS)