adding in submeshes and multiple materials into Canvas Mesh Element

[grayclee]

Describe the problem

In the canvas mesh element script I can only have one mesh with one materials
the 3D element is one mesh but it needs support for multiple materials

A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
I cannot add multiple materials into the script. This was discovered while scrolling and the cursor wasn't masking properly

Describe the solution you'd like

added material support
A clear and concise description of what you want to happen.

Describe alternatives you've considered

A clear and concise description of any alternative solutions or features you've considered.

Additional context

Add any other context or screenshots about the feature request here.