Fix convertShape to use getMeshPath

[gilwoolee]

This PR fixes rviz::convertShape(MeshShape...) method to use getMeshPath instead of getMeshUri for meshUri.
When a mesh is loaded via MeshShape, convertShape(MeshShape...) gets called. Since meshUri is used by Rviz, it has to be a raw filepath, which is not the case when using getMeshUri.

This was never an issue with Herb or Ada because we use urdfLoader and it constructs AssimpMesh, which doesn't call this function. It was discovered while @vinitha910 was trying to load cozmo mesh directly using raw filepaths.

It has been tested by constructing cozmo with MeshShapes and visualizing it in Rviz through aikido InteractiveViewer.

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[brianhou]

LGTM, minor changes

[jslee02]

Looks good to me. The suggestions from @brianhou sound good to me as well.

[codecov]

Codecov Report

Merging #518 into master will not change coverage.
The diff coverage is n/a.

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