[C++][Parquet] Wrong variant extension name

[HuaHuaY]

Describe the bug, including details regarding any error messages, version, and platform.

The extension name of variant is set to parquet.variant but arrow's specification requires arrow.parquet.variant. https://arrow.apache.org/docs/format/CanonicalExtensions.html#parquet-variant

// cpp/src/parquet/arrow/variant_internal.h:49

class PARQUET_EXPORT VariantExtensionType : public ::arrow::ExtensionType {
 public:
  explicit VariantExtensionType(const std::shared_ptr<::arrow::DataType>& storage_type);

  std::string extension_name() const override { return "parquet.variant"; }

  bool ExtensionEquals(const ::arrow::ExtensionType& other) const override;

Component(s)

Parquet, C++