prepass vertex shader always outputs world position (#10657)

# Objective

the pbr prepass vertex shader currently only sets
`VertexOutput::world_position` when deferred or motion prepasses are
enabled.
the field is always in the vertex output so is otherwise undetermined,
and the calculation is very cheap.

## Solution

always set the world position in the pbr prepass vert shader.

crates/bevy_pbr/src/prepass/prepass.wgsl

@@ -89,9 +89,7 @@ fn vertex(vertex_no_morph: Vertex) -> VertexOutput {
     out.color = vertex.color;
 #endif
 
-#ifdef MOTION_VECTOR_PREPASS_OR_DEFERRED_PREPASS
     out.world_position = mesh_functions::mesh_position_local_to_world(model, vec4<f32>(vertex.position, 1.0));
-#endif // MOTION_VECTOR_PREPASS_OR_DEFERRED_PREPASS
 
 #ifdef MOTION_VECTOR_PREPASS
     // Use vertex_no_morph.instance_index instead of vertex.instance_index to work around a wgpu dx12 bug.