Custom Doxygen executable to improve Sphinx builds

[MathiasMagnus]

This PR improves how Sphinx docs are built, specifically those using rocm-docs-core.

Changes

• Updates the documentation of rocm_add_sphinx_doc (which even had it's name outdated.
• Adds more validation of parameters and feedback to users who misuse the function.
• Adds search of Doxygen executable
  • Defines an opt-in flag USE_DOXYGEN which triggers a poor man's version of REQUIRED for the Doxygen executable. It relays the full path of Doxygen to rocm-docs-core as enabled by this PR.
• Adds a simple positive test of this function while previously there was none.

Notes

• The requirements.in will need a change once the dependent PR of rocm-docs-core goes live and receives a tagged version.

[MathiasMagnus]

My only concern at present is adding BUILDER as a mandatory argument, I worry that will cause issues for backwards compatibility. I would prefer that this variable have a sane default (perhaps html?), but am open to arguments.

@lawruble13 BUILDER being mandatory hasn't changed. While the docs suggested it isn't mandatory, the internal logic just assumed it exists. I just clarified it instead of letting it blow up in the users' face.

[MathiasMagnus]

@saadrahim Should be okay.

[pramenku]

This change is causing MiGraphX failed to compile.

Do we need to install any pre-req @pfultz2 ?

11:18:25 -- MIGraphx is using Find-2.0 API of MIOpen 11:18:25 -- MIGraphx is using Find Mode API of MIOpen 11:18:25 CMake Error at /opt/rocm/share/rocm/cmake/ROCMSphinxDoc.cmake:10 (find_program): 11:18:25 Could not find SPHINX_EXECUTABLE using the following names: sphinx-build 11:18:25 Call Stack (most recent call first): 11:18:25 docs/CMakeLists.txt:27 (include) 11:18:25

Command to build MigraphX

pip3 install https://github.com/RadeonOpenCompute/rbuild/archive/master.tar.gz && git clone --depth=1 https://github.com/ROCmSoftwarePlatform/AMDMIGraphX --branch master && cd AMDMIGraphX && rbuild package --cxx /opt/rocm/llvm/bin/clang++ -DGPU_TARGETS="gfx906;gfx908;gfx90a;gfx1030;gfx1100;gfx1101;gfx1102" -d /workspace/AMDMIGraphX/deps -B /workspace/AMDMIGraphX/build'

[pramenku]

python3 -m pip install sphinx -> After installation, it's passing

But, @pfultz2 has patch https://github.com/RadeonOpenCompute/rocm-cmake/pull/144 which will help us. Can we get this PR merged in https://github.com/RadeonOpenCompute/rocm-cmake/tree/release-staging/rocm-rel-6.0 branch too so that it will come to 6.0 Mainline.