fix: Only add build type to CMAKE_LIBRARY_OUTPUT_DIRECTORY if needed

[trxcllnt]

This PR only appends CMAKE_BUILD_TYPE to CMAKE_LIBRARY_OUTPUT_DIRECTORY if the build dir path doesn't already end with the build type.

Maintaining parallel build trees for release/debug can reduce rebuild times when switching between configs*.

If a user wishes to configure this way today, cmake-js defines a nonsense path for LIBRARY_OUTPUT_DIRECTORY:

npx cmake-js -D -O build/Debug
# -DCMAKE_LIBRARY_OUTPUT_DIRECTORY=build/Debug/Debug

npx cmake-js -O build/Release
# -DCMAKE_LIBRARY_OUTPUT_DIRECTORY=build/Release/Release

I assume this is to align with node-gyp and require('bindings')('foo.node'), which this PR would still support.

If the user configured into build/${cmake_build_type}, the LIBRARY_OUTPUT_DIRECTORY should be ${cmake_binary_dir}, not ${cmake_binary_dir}/{cmake_build_type}.

* An alternative could be to customize the location of the object files based on build type... but this isn't supported by CMake 🙁.