[leveldb] Install util header files

Hi !

I'm the maintainer of vcpkg , when I'm working on [issues ](https://github.com/microsoft/vcpkg/issues/18493)about leveldb :
The leveldb library is installed, but only include/leveldb is included, there is no util


I submitted a pr :
https://github.com/microsoft/vcpkg/pull/22650

As a solution, the util headers need to be exported for consumer use, but It looks like these header files are intended to be private (https://github.com/google/leveldb/blob/main/CMakeLists.txt), so could you please confirm that you want these util headers to be available to consumers?