Changed namespace fix to use Sphinx autodoc-process-* events

[timohl]

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

Open3D uses namespaces open3d.cpu.pybind. and open3d.cuda.pybind. to differentiate between both device builds.
This adds a lot of clutter to the documentation (see screenshots below).
There is already a partial fix for functions documented using docstring::ClassMethodDocInject and docstring::FunctionDocInject.
However, a big part of Open3D does not use those functions for documentation and #7081 removed those from the contribute docs (so they should probably be avoided in the future).

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

This PR moves the namespace fix away from docstring::ClassMethodDocInject and docstring::FunctionDocInject to the sphinx documentation generation.
It uses the autodoc events autodoc-process-signature and autodoc-process-docstring to change namespaces to open3d. during doc generation.
With this PR all namespaces are fixed in the documentation (checked using the search function).

This is a fix used in #6917 since mypy would complain about missing imports for functions with fixed namespaces.

Notice in the following before/after screenshots that the namespaces in the clear function were already fixed due to using docstring::ClassMethodDocInject. This PR improves the namespaces in __init__ and as_tensor though, resulting in better readability.

Here before:

and after:

[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.

[timohl]

Documentation CI was already failing in previous commits.
With the following error:

The following packages have unmet dependencies:
 cmake : Depends: libssl1.1 (>= 1.1.1) but it is not installable

The following is the function installing docs dependencies.
Maybe an issue in the kitware repository?
Not sure why this is even required.
Why not use the cmake from ubuntu repositories?

Open3D/util/ci_utils.sh

Lines 338 to 375 in 0ae7b1a

	# Install dependencies needed for building documentation (on Ubuntu 20.04)
	# Usage: install_docs_dependencies "${OPEN3D_ML_ROOT}"
	install_docs_dependencies() {
	echo
	echo Install ubuntu dependencies
	echo Update cmake needed in Ubuntu 20.04
	sudo apt-key adv --fetch-keys https://apt.kitware.com/keys/kitware-archive-latest.asc
	sudo apt-add-repository --yes 'deb https://apt.kitware.com/ubuntu/ focal main'
	./util/install_deps_ubuntu.sh assume-yes
	sudo apt-get install --yes cmake
	sudo apt-get install --yes libxml2-dev libxslt-dev python3-dev
	sudo apt-get install --yes doxygen
	sudo apt-get install --yes texlive
	sudo apt-get install --yes texlive-latex-extra
	sudo apt-get install --yes ghostscript
	sudo apt-get install --yes pandoc
	sudo apt-get install --yes ccache
	echo
	echo Install Python dependencies for building docs
	command -v python
	python -V
	python -m pip install -U -q "wheel==$WHEEL_VER" \
	"pip==$PIP_VER"
	python -m pip install -U -q "yapf==$YAPF_VER"
	if [[ -d "$1" ]]; then
	OPEN3D_ML_ROOT="$1"
	echo Installing Open3D-ML dependencies from "${OPEN3D_ML_ROOT}"
	python -m pip install -r "${OPEN3D_ML_ROOT}/requirements.txt"
	python -m pip install -r "${OPEN3D_ML_ROOT}/requirements-torch.txt"
	python -m pip install -r "${OPEN3D_ML_ROOT}/requirements-tensorflow.txt"
	else
	echo OPEN3D_ML_ROOT="$OPEN3D_ML_ROOT" not specified or invalid. Skipping ML dependencies.
	fi
	echo
	python -m pip install -r "${OPEN3D_SOURCE_ROOT}/python/requirements.txt"
	python -m pip install -r "${OPEN3D_SOURCE_ROOT}/python/requirements_jupyter_build.txt"
	python -m pip install -r "${OPEN3D_SOURCE_ROOT}/docs/requirements.txt"
	}

[benjaminum]

@timohl This is great! Thanks!

We are moving away from the *Inject functions to simplify writing docstrings.