[cmake] Allow users to link against onemath_<domain>_<backend> targets

[Rbiessy]

Description

The goal of this PR is to allow users to integrate oneMath in their application with compile-time dispatching, only by linking against onemath__ targets. With the current CMake this would fail to compile due to missing include directories and linking libraries unless users manually add the dependencies or set up environment variables. This makes it easier for users.
To show this I have also updated the example's CMake to simplify them and make sure they only rely on target_link_libraries to get the oneMath library dependencies.

Other changes:

• Remove mention of onemath_ targets in the documentation. I believe these targets only provide partial support for runtime-dispatching and have not benefit over using onemath.
• Remove occurrences of install(TARGETS ${LIB_OBJ} ...). These target pollute the outputted oneMathTargets.cmake file and end up requiring more CMake targets such as ONEMATH::cublas targets which are not useful to users. With these changes ${LIB_NAME} targets link ${LIB_OBJ} targets privately so it is not needed to install them anymore.

These are only CMake changes so I think the review from onemath-arch-write is enough but more feedback is welcomed.

Checklist

All Submissions

• Do all unit tests pass locally?
  • ctest_mklcpu_mklgpu.txt
  • mklcpu_cuda_ct_examples.txt
  • cuda_examples.txt
  • hip_examples.txt