Remove extra documentation build for python examples

[saurabheights]

Type

• Bug fix (non-breaking change which fixes an issue): Fixes #
• New feature (non-breaking change which adds functionality). Resolves #
• Breaking change (fix or feature that would cause existing functionality to not work as expected) Resolves #

Motivation and Context

Speeds up building C++ documentation during development of C++ code.

Additionally, printing output path allows quick checking from local system. P.S. Will it be ok to print file uri instead of file path, i.e.

file:///home/sk/workspace/open3d_prs/Open3D/docs/_out/html/index.html instead of /home/sk/workspace/open3d_prs/Open3D/docs/_out/html/index.html. The former will be clickable on bash.

Checklist:

• I have run python util/check_style.py --apply to apply Open3D code style
  to my code.
• This PR changes Open3D behavior or adds new functionality.
  • Both C++ (Doxygen) and Python (Sphinx / Google style) documentation is
    updated accordingly.
  • I have added or updated C++ and / or Python unit tests OR included test
    results (e.g. screenshots or numbers) here.
• I will follow up and update the code if CI fails.
• For fork PRs, I have selected Allow edits from maintainers.

Description

[update-docs]

Thanks for submitting this pull request! The maintainers of this repository would appreciate if you could update the CHANGELOG.md based on your changes.

[ssheorey]

Yes, should be fine to replace output docs path with URL.

Thanks! LGTM.

[ssheorey]

Hi @saurabheights something is not quite right with the updates:

• The generated docs are only 210MB compared to >400MB earlier.
• Core, Geometry (Tensor), Pipelines and Tensor pipelines tutorials are blank.
• There are some Python errors during the sphinx run, starting from:
  • https://github.com/isl-org/Open3D/actions/runs/6908435912/job/18797725788?pr=6487#step:8:7421

[saurabheights]

@ssheorey Found the issue, the methods that I put inside args.sphinx are actually called without passing sphinx flag - https://github.com/isl-org/Open3D/actions/runs/6908435912/job/18797725788?pr=6487#step:8:5334. Give me a few days. I will go through workflow files to ensure the fix is done correctly.

Thanks for catching this.

[saurabheights]

@ssheorey Well, the fix is to revert that commit. Running doxygen Doxyfile is actually the fastest way to generate C++ docs, which was already documented. Apologies for the oversight.

1. I have pushed another minor commit to skip double build of examples. For example, here rst are built twice -
   https://github.com/isl-org/Open3D/actions/runs/6878798533/job/18801576929?pr=6414#step:8:5448
   https://github.com/isl-org/Open3D/actions/runs/6878798533/job/18801576929?pr=6414#step:8:7007

2. Found a stale documentation issue - When the documentation is moved, it seams that the old path of file is not removed -
   http://www.open3d.org/docs/latest/tutorial/geometry/voxelization.html#Voxel-carving which has latest 2a11e0e version
   http://www.open3d.org/docs/latest/tutorial/Advanced/voxelization.html#Voxel-carving which has very old 664eff5 version.

 * 664eff507 Wed Sep 30 21:30:43 2020 -0700 Yixing Lao Refector some image tests failing on arm simulator (#2393)

The README.md mentions unpack_docs.sh but I dont think this file is committed. My guess is on the deployment server, the new docs file are being copied to deployment location without cleaning up old docs in disk.