Display bounding boxes on unloaded payloads

**Is your feature request related to a problem? Please describe.**

I'm trying to get bounding boxes to display for unloaded payloads using the extents hints attribute, following the example from the [USD Cookbook](https://github.com/ColinKennedy/USD-Cookbook/blob/33eac067a0a62578934105b19a2b9d8e4ea0646c/references/extents_hint_and_bounding_boxes/README.md).

This works as advertised in USDview. It does not work in Maya, and unloading a payload shows nothing in the viewport.

**Describe the solution you'd like**

Get bounding boxes to display for unloaded payloads using the extents hints attribute.

**Describe alternatives you've considered**

I would imagine that this might be something that would work in Hydra, but not in VP2. Of course, it would be nice if it worked in both. Currently, it appears to work in neither.

**Additional context**

Regarding Hydra, this issue may be related from OpenUSD:
"[Storm not drawing unloaded payload boxes #2720](https://github.com/PixarAnimationStudios/OpenUSD/issues/2720)"

Start by reproducing the USD Cookbook extents-hints example in Maya with a payload unloaded, then compare behavior in USDview, VP2, and Hydra. Review the related OpenUSD issue #2720 for Hydra context. Done means the extents-hint bounding boxes are visible for unloaded payloads in the supported viewport(s).

Written by the indexing model from the issue text.