apacheGH-43578: [C++] Simplify arrow::ArrayStatistics::ValueType

We can cover integer values by `int64_t` and `uint64_t` and float
values by `double`.

We can remove `std::string_view` because we don't support out of
`ArrayStatistics` string/binary data.

cpp/src/arrow/array/statistics.h

@@ -34,9 +34,7 @@ namespace arrow {
 /// as Apache Parquet may have statistics. Statistics associated with
 /// data source can be read unified API via this class.
 struct ARROW_EXPORT ArrayStatistics {
-  using ValueType =
-      std::variant<bool, int8_t, uint8_t, int16_t, uint16_t, int32_t, uint32_t, int64_t,
-                   uint64_t, util::Float16, float, double, std::string, std::string_view>;
+  using ValueType = std::variant<bool, int64_t, uint64_t, double, std::string>;
 
   ArrayStatistics() = default;
   ~ArrayStatistics() = default;

cpp/src/arrow/array/statistics_test.cc

@@ -41,11 +41,11 @@ TEST(ArrayStatisticsTest, TestMin) {
   ArrayStatistics statistics;
   ASSERT_FALSE(statistics.min.has_value());
   ASSERT_FALSE(statistics.is_min_exact.has_value());
-  statistics.min = static_cast<int32_t>(29);
+  statistics.min = static_cast<uint64_t>(29);
   statistics.is_min_exact = true;
   ASSERT_TRUE(statistics.min.has_value());
-  ASSERT_TRUE(std::holds_alternative<int32_t>(statistics.min.value()));
-  ASSERT_EQ(29, std::get<int32_t>(statistics.min.value()));
+  ASSERT_TRUE(std::holds_alternative<uint64_t>(statistics.min.value()));
+  ASSERT_EQ(29, std::get<uint64_t>(statistics.min.value()));
   ASSERT_TRUE(statistics.is_min_exact.has_value());
   ASSERT_TRUE(statistics.is_min_exact.value());
 }
@@ -79,19 +79,19 @@ TEST(ArrayStatisticsTest, TestEquality) {
   statistics2.distinct_count = 2929;
   ASSERT_EQ(statistics1, statistics2);
 
-  statistics1.min = std::string_view("world");
+  statistics1.min = std::string("world");
   ASSERT_NE(statistics1, statistics2);
-  statistics2.min = std::string_view("world");
+  statistics2.min = std::string("world");
   ASSERT_EQ(statistics1, statistics2);
 
   statistics1.is_min_exact = false;
   ASSERT_NE(statistics1, statistics2);
   statistics2.is_min_exact = false;
   ASSERT_EQ(statistics1, statistics2);
 
-  statistics1.max = arrow::util::Float16(-29);
+  statistics1.max = -29;
   ASSERT_NE(statistics1, statistics2);
-  statistics2.max = arrow::util::Float16(-29);
+  statistics2.max = -29;
   ASSERT_EQ(statistics1, statistics2);
 
   statistics1.is_max_exact = true;