fix compilation error on apple-clang 15

[toge]

I met compilation error on apple-clang 15.
Error messages are following:

In file included from table/block_based/block_based_table_builder.cc:10:
In file included from table/block_based/block_based_table_builder.h:17:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.5.sdk/usr/include/c++/v1/vector:321:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.5.sdk/usr/include/c++/v1/__format/formatter_bool.h:20:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.5.sdk/usr/include/c++/v1/__format/formatter_integral.h:32:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.5.sdk/usr/include/c++/v1/locale:202:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.5.sdk/usr/include/c++/v1/__locale:15:
In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.5.sdk/usr/include/c++/v1/__memory/shared_ptr.h:31:
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.5.sdk/usr/include/c++/v1/__memory/unique_ptr.h:66:19: error: invalid application of 'sizeof' to an incomplete type 'rocksdb::BlockBasedTableBuilder::ParallelCompressionRep'
    static_assert(sizeof(_Tp) >= 0, "cannot delete an incomplete type");
                  ^~~~~~~~~~~
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.5.sdk/usr/include/c++/v1/__memory/unique_ptr.h:300:7: note: in instantiation of member function 'std::default_delete<rocksdb::BlockBasedTableBuilder::ParallelCompressionRep>::operator()' requested here
      __ptr_.second()(__tmp);
      ^
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX14.5.sdk/usr/include/c++/v1/__memory/unique_ptr.h:266:75: note: in instantiation of member function 'std::unique_ptr<rocksdb::BlockBasedTableBuilder::ParallelCompressionRep>::reset' requested here
  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX23 ~unique_ptr() { reset(); }
                                                                          ^
table/block_based/block_based_table_builder.cc:448:3: note: in instantiation of member function 'std::unique_ptr<rocksdb::BlockBasedTableBuilder::ParallelCompressionRep>::~unique_ptr' requested here
  Rep(const BlockBasedTableOptions& table_opt, const TableBuilderOptions& tbo,
  ^
table/block_based/block_based_table_builder.h:162:10: note: forward declaration of 'rocksdb::BlockBasedTableBuilder::ParallelCompressionRep'
  struct ParallelCompressionRep;
         ^

This issue is caused by the positions defined between BlockBasedTableBuilder::Rep and BlockBasedTableBuilder::ParallelCompressionRep.
This PR switches these positions to resolve this issue.

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[pengybhnu]

I met the same compilation error too on Ubuntu clang version 19 to compile rocksdb any version 9.x.x from conan package or git clone from this repository. I had to modify struct BlockBasedTableBuilder::ParallelCompressionRep to struct BlockBasedTableBuilder::Rep ahead and compile modified source and link local libary in my project. Is the issue fixed PR merged to the newest version ? @toge