Move to Ubuntu 22.04, build shared libraries by default, simplified (smaller) python package.

[ssheorey]

Cherry-picks the shared-library-by-default and pybind-simplification work from copilot/separate-pybind-and-libopen3d without the host/device (libOpen3D vs libOpen3D_cuda/xpu) library split.

• Update CI to Ubuntu 22.04. 20.04 is EOL.
• BUILD_SHARED_LIBS now defaults to ON. Python package now uses a shared open3d library.
• Single open3d.pybind module; CUDA/SYCL detected at runtime via core.cuda.is_available()/core.sycl.is_available() instead of shipping separate cpu/cuda package variants.
• Device strings accept a bare type name (e.g. "cuda"), defaulting id to 0.
• New utility::filesystem::GetSelfBinaryDirectory() helper; Logging.cpp print function is now a function-local static.
• Renamed pybind/core/tensor_type_caster -> type_caster and added an implicit Device<->str caster.
• Flattened ML custom-op output layout (no cpu/cuda subfolder) and fixed the torch/tf ops loaders to match.
• Fixed a static-link ordering bug (curl/BoringSSL) exposed by building Open3D as a shared library, using CMake's LINK_GROUP:RESCAN genex.
• Updated docs/compilation.rst to describe the dependency constraints while building Open3D.

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

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.