Method null_remaining

cpp/src/arrow/util/rle_encoding_internal.h:871–874

  constexpr size_type null_read() const noexcept { return null_read_; }

  constexpr size_type null_remaining() const noexcept {
    ARROW_DCHECK_LE(null_read_, null_count_);
    return null_count_ - null_read_;
  }

  constexpr void AccrueReadNulls(size_type to_read) noexcept {
    ARROW_DCHECK_LE(to_read, null_remaining());