[Bug]: Reference of spark and java in website is missing

[Thespica]

Is there an existing issue for this?

• I have searched the existing issues

Current Behavior

As titile.

Expected Behavior

displaying scaladoc and javadoc

Minimal Reproducible Example

Environment

• Operating system:
• GraphAr version:

Link to GraphAr Logs

No response

Further Information

scala: invalid output arguments -DoutputDirectory. Keep original way to generate docs.

java: use whitespace rather than tab in makefile, which may leads problems.

[acezen]

refer to html generate process: https://github.com/alibaba/GraphAr/blob/c752915bb4a8842423d91481def089e873712b7d/docs/Makefile#L53-L57

seems that the process generate api-doc of c++/java/spark before SPHINXBUILD, so the _build/html directory is not existed yet in api-doc process, and failed to generate to the directory.

The better solution is make html generate process build SPHINXBUILD first and then build the api-doc document.