Batch together shadow view draws for different materials with the same conceptual shaders

## What problem does this solve or what need does it fill?

Entities with different materials get put in separate draw batches.

For shadow views (or depth-only prepass, but that's often niche), this is often an unnecessary constraint. Even if they have different bindings and shaders for the main pass shading, different materials often have the same shader for depth-only output like the shadow pass, and could be batched together.

## What solution would you like?

Batch together shadow view draws for entities with different materials, where possible.

## Additional context

Previously attempted in https://github.com/bevyengine/bevy/pull/11647

Review the previously attempted PR #11647 first, then trace how shadow-view and depth-only draws are currently batched for entities with different materials. The work is done when compatible draws using the same conceptual shaders can share a batch without changing main-pass material behavior.

Written by the indexing model from the issue text.