ID 380272 - Hydra Viewer: Visual artifacts when using ambient occlusion

 Issue occurred after upgrading to USD 19.01

Problem summary:

When using the ambient occlusion option in a multipane Hydra viewport, when using the persp camera, and scrolling around the viewport, visual glitches will appear on the geometry. 

The effect can be lessened by changing the viewerSettings.persp.near and far attributes on the project settings tab, but is still fairly obvious at all usable clipping depths.

Steps to reproduce:

1. Open attached project: xxx.katana
2. Expand the scene from the merge node
3. set a Hydra viewer to a multipane layout, and turn on ambient occlusion
4. in one of the panes, look through the persp cam and move around.

Expected behaviour:

Ambient occlusion is displayed correctly in each viewport.

Actual behaviour:

Certain viewports show visual artifacts around vertices of the geometry

Tested versions/platforms:

• 3.1v2 - Unaffected
• 3.2_cmake_usd - Affected