Add some legacy warppers for Tensor PointCloud

[yuecideng]

This PR adds wrapper for FarthestPointDownSample, HiddenPointRemoval and SegmentPlane to tensor PointCloud.

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This change is 

[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.

[yxlao]

For non-CPU point cloud, we shall first copy to host, process, and copy back.

[ssheorey]

For all wrappers over legacy functions, mention in both C++ and Python docs that only CPU device is supported and CUDA data will be copied to the CPU for processing. Also mention which attributes are preserved by the operation.

In pybind code, document return values and add a brief example. See cluster dbscan as an example.

Reviewable status: 0 of 4 files reviewed, 4 unresolved discussions (waiting on @reyanshsolis and @yuecideng)

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cpp/open3d/t/geometry/PointCloud.h line 402 at r3 (raw file):

    /// \param camera_location All points not visible from that location will be
    /// removed.
    /// \param radius The radius of the spherical projection.

Add docs for return value (\return)

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cpp/open3d/t/geometry/PointCloud.cpp line 858 at r3 (raw file):

            TriangleMesh::FromLegacy(*lmesh, GetPointPositions().GetDtype(),
                                     core::Int64, GetDevice()),
            core::Tensor(indices, {(int64_t)indices.size()}, core::Int64,

Use core::Tensor(std::move(indices)).To(GetDevice()) (Tensor ctor that takes ownership of vector data). This will prevent a copy if data is on the CPU.

Since we know the indices of the retained points, copy over all point attributes for the retained points.

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cpp/open3d/t/geometry/PointCloud.cpp line 892 at r3 (raw file):

    return std::make_tuple(
            core::eigen_converter::EigenMatrixToTensor(plane).Flatten(),
            core::Tensor(indices, {(int64_t)indices.size()}, core::Int64,

Use core::Tensor(std::move(indices)).To(GetDevice()) (Tensor ctor that takes ownership of vector data). This will prevent a copy if data is on the CPU.

[yuecideng]

I tried to update the docs in pybind file. Please see whether it is acceptable.

Reviewable status: 0 of 4 files reviewed, 4 unresolved discussions (waiting on @reyanshsolis, @ssheorey, and @yuecideng)

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cpp/open3d/t/geometry/PointCloud.h line 402 at r3 (raw file):

Previously, ssheorey (Sameer Sheorey) wrote…

Add docs for return value (\return)

Done.

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cpp/open3d/t/geometry/PointCloud.cpp line 858 at r3 (raw file):

Previously, ssheorey (Sameer Sheorey) wrote…

Use core::Tensor(std::move(indices)).To(GetDevice()) (Tensor ctor that takes ownership of vector data). This will prevent a copy if data is on the CPU.

Since we know the indices of the retained points, copy over all point attributes for the retained points.

Done.

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cpp/open3d/t/geometry/PointCloud.cpp line 892 at r3 (raw file):

Previously, ssheorey (Sameer Sheorey) wrote…

Use core::Tensor(std::move(indices)).To(GetDevice()) (Tensor ctor that takes ownership of vector data). This will prevent a copy if data is on the CPU.

Done.