Fix panic in custom_render_phase example

[rparrett]

Objective

Fix panic in custom_render_phase.

This example was broken by #17764, but that breakage evolved into a panic after #17849. This new panic seems to illustrate the problem in a pretty straightforward way.

2025-02-15T00:44:11.833622Z  INFO bevy_diagnostic::system_information_diagnostics_plugin::internal: SystemInfo { os: "macOS 15.3 Sequoia", kernel: "24.3.0", cpu: "Apple M4 Max", core_count: "16", memory: "64.0 GiB" }    
2025-02-15T00:44:11.908328Z  INFO bevy_render::renderer: AdapterInfo { name: "Apple M4 Max", vendor: 0, device: 0, device_type: IntegratedGpu, driver: "", driver_info: "", backend: Metal }
2025-02-15T00:44:12.314930Z  INFO bevy_winit::system: Creating new window App (0v1)
thread 'Compute Task Pool (1)' panicked at /Users/me/src/bevy/crates/bevy_ecs/src/system/function_system.rs:216:28:
bevy_render::batching::gpu_preprocessing::batch_and_prepare_sorted_render_phase<custom_render_phase::Stencil3d, custom_render_phase::StencilPipeline> could not access system parameter ResMut<PhaseBatchedInstanceBuffers<Stencil3d, MeshUniform>>

Solution

Add a SortedRenderPhasePlugin for the custom phase.

Testing

cargo run --example custom_render_phase