Allow setting view status from json string

[yxlao]

This PR allows setting view status from a json string. This allows setting the visualizer to the exact same view points.

Example usage:

1. Launch the Open3D visualizer (legacy)
2. Press ctrl+c to copy the view status as a json string
3. As an example, in a new visualizer, you can use the following code to set the view status

   vis = o3d.visualization.Visualizer()
   vis.create_window()
   vis.add_geometry(mesh)
   vis.update_geometry(mesh)
   vis.set_view_status(view_status_str)  # view_status_str is the json string
   vis.poll_events()
   vis.update_renderer()
   buffer = vis.capture_screen_float_buffer()
   vis.destroy_window()

Changes:

• Visualizer::CopyViewStatusToClipboard(): unchanged
• Visualizer::CopyViewStatusFromClipboard(): unchanged
• Visualizer::GetViewStatus(): added
• SetViewStatus(const std::string &view_status_str): added

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.
  • (N/A) Both C++ (Doxygen) and Python (Sphinx / Google style) documentation is
    updated accordingly.
  • (N/A) 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

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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.