Copy SampleCount when making a copy of FilamentView

[patrikhuber]

If that function doesn't copy the sample count, the copied view will not be an exact copy - it'll contain the default sample count (=4), and not the sample count of the view it's copying from.

Type

• Bug fix (non-breaking change which fixes an issue): Fixes - separate issue not created, just see above problem & fix

Motivation and Context

See above.

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

See above.

[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]

Looks good @patrikhuber Thanks!