Summary:
We observed `CompactionOutputs::UpdateGrandparentBoundaryInfo` consumes much time for `InternalKey::DecodeFrom` and `InternalKey::~InternalKey` in flame graph.

This PR omit the InternalKey object in `CompactionOutputs::UpdateGrandparentBoundaryInfo` .

![image](https://github.com/facebook/rocksdb/assets/1574991/661eaeec-2f46-46c6-a6a8-9738d6c191de)

Pull Request resolved: https://github.com/facebook/rocksdb/pull/11610

Reviewed By: ajkr

Differential Revision: D47426971

Pulled By: cbi42

fbshipit-source-id: f0d3a8186d778294515c0685032f5b395c4d6a62