GH-45947: [C++][Parquet] Variant encoding

Author: qzyu999

cpp/src/arrow/CMakeLists.txt

@@ -391,6 +391,7 @@ set(ARROW_SRCS
     extension/bool8.cc
     extension/json.cc
     extension/parquet_variant.cc
+    extension/variant_builder.cc
     extension/variant_internal.cc
     extension/uuid.cc
     pretty_print.cc

cpp/src/arrow/extension/CMakeLists.txt

@@ -16,7 +16,7 @@
 # under the License.
 
 set(CANONICAL_EXTENSION_TESTS bool8_test.cc json_test.cc uuid_test.cc
-                              variant_internal_test.cc)
+                              variant_internal_test.cc variant_builder_test.cc)
 
 if(ARROW_JSON)
   list(APPEND CANONICAL_EXTENSION_TESTS tensor_extension_array_test.cc opaque_test.cc)

cpp/src/arrow/extension/meson.build

@@ -15,7 +15,8 @@
 # specific language governing permissions and limitations
 # under the License.
 
-canonical_extension_tests = ['bool8_test.cc', 'json_test.cc', 'uuid_test.cc', 'variant_internal_test.cc']
+canonical_extension_tests = ['bool8_test.cc', 'json_test.cc', 'uuid_test.cc',
+                             'variant_internal_test.cc', 'variant_builder_test.cc']
 
 if needs_json
     canonical_extension_tests += [