3D projections. (Cameras, Procedurals & Textures)

**Is your feature request related to a problem? Please describe.**
Planar, Spherical and Perspective shading node projections are all needed in the day-to-day work of Maya Layout & Lighting artists.

**Describe the solution you'd like**
Projection node with input transform promoted to a shading graph.

**Describe alternatives you've considered**
Ideally implemented as MaterialX node connecting an input USD XForm (animatable).
See tri-planar node:
https://github.com/AcademySoftwareFoundation/MaterialX/blob/main/documents/Specification/MaterialX.Specification.md#texture-nodes

**Additional context**
Maya has powerful projection placement with many types. All would be ideal but **Planar**, **Spherical** and **Perspective** projections are the most essential.

Start by reading the linked MaterialX specification's texture-nodes section and the issue's requirements for planar, spherical, and perspective projections. Define the implementation scope around a shading-graph projection node with an animatable USD XForm input; the issue names no repository files or tests, so those entry points must be located before work begins.

Written by the indexing model from the issue text.