Export tonemapping_pipeline_key (2d), alpha_mode_pipeline_key (#11166)

This expands upon #11134.

I found myself needing `tonemapping_pipeline_key` for some custom 2d
draw functions. #11134 exported the 3d version of
`tonemapping_pipeline_key` and this PR exports the 2d version. I also
made `alpha_mode_pipeline_key` public for good measure.

Author: brianreavis

crates/bevy_pbr/src/material.rs

@@ -404,7 +404,7 @@ impl<P: PhaseItem, M: Material, const I: usize> RenderCommand<P> for SetMaterial
 
 pub type RenderMaterialInstances<M> = ExtractedInstances<AssetId<M>>;
 
-const fn alpha_mode_pipeline_key(alpha_mode: AlphaMode) -> MeshPipelineKey {
+pub const fn alpha_mode_pipeline_key(alpha_mode: AlphaMode) -> MeshPipelineKey {
     match alpha_mode {
         // Premultiplied and Add share the same pipeline key
         // They're made distinct in the PBR shader, via `premultiply_alpha()`

crates/bevy_sprite/src/mesh2d/material.rs

@@ -354,7 +354,7 @@ impl<P: PhaseItem, M: Material2d, const I: usize> RenderCommand<P>
     }
 }
 
-const fn tonemapping_pipeline_key(tonemapping: Tonemapping) -> Mesh2dPipelineKey {
+pub const fn tonemapping_pipeline_key(tonemapping: Tonemapping) -> Mesh2dPipelineKey {
     match tonemapping {
         Tonemapping::None => Mesh2dPipelineKey::TONEMAP_METHOD_NONE,
         Tonemapping::Reinhard => Mesh2dPipelineKey::TONEMAP_METHOD_REINHARD,