Specialization keys `VIEW_PROJECTION_*` in depth prepass for shadow maps

[Lichtso]

Bevy version and features

Version: v0.16.1
Only default features

What you did

Created a custom material pipeline which has two very different code paths depending on perspective vs. orthographic projections because it involves billboards and ray tracing. I am aware of the existence of the view_is_orthographic runtime check, but would have liked to use the pipeline specialization for that instead, especially since they work in the "normal" forward pass.

What went wrong

The specialization keys VIEW_PROJECTION_PERSPECTIVE, VIEW_PROJECTION_ORTHOGRAPHIC, VIEW_PROJECTION_NONSTANDARD are only set for camera views:

• https://github.com/bevyengine/bevy/blob/ec735b9649e21e70cf240c15bb2a95e92b242b08/crates/bevy_pbr/src/meshlet/material_pipeline_prepare.rs#L105C9-L111C10
• https://github.com/bevyengine/bevy/blob/ec735b9649e21e70cf240c15bb2a95e92b242b08/crates/bevy_pbr/src/render/mesh.rs#L381C9-L387C10

But not in shadow views:

• https://github.com/bevyengine/bevy/blob/ec735b9649e21e70cf240c15bb2a95e92b242b08/crates/bevy_pbr/src/render/light.rs#L1964C13-L1986C15

• bevy/crates/bevy_pbr/src/render/light.rs

  Line 1728 in ec735b9

  let mut light_key = MeshPipelineKey::DEPTH_PREPASS;

or where ever it might go.