Custom shader causes excessive number of rendering commands

Steps to reproduce:

1. Open the UI Builder and create
2. Add one root element as a container with 10 text elements inside
3. Open the UI Toolkit debugger and enable "Draw Stats Overlay"
4. Read the number of "Material sets"
5. Assign a material on the container
6. Read the number of "Material sets"

Actual results: 

Increases by 1

Expected results: 

Increases by 12
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