Update docs to use MATERIAL_BIND_GROUP (#20458)

# Objective

- Make the docs consistent with the shaders

## Solution

- Fix them

## Testing

- its docs

Author: atlv24

crates/bevy_pbr/src/material.rs

@@ -124,9 +124,9 @@ pub const MATERIAL_BIND_GROUP_INDEX: usize = 3;
 /// In WGSL shaders, the material's binding would look like this:
 ///
 /// ```wgsl
-/// @group(3) @binding(0) var<uniform> color: vec4<f32>;
-/// @group(3) @binding(1) var color_texture: texture_2d<f32>;
-/// @group(3) @binding(2) var color_sampler: sampler;
+/// @group(#{MATERIAL_BIND_GROUP}) @binding(0) var<uniform> color: vec4<f32>;
+/// @group(#{MATERIAL_BIND_GROUP}) @binding(1) var color_texture: texture_2d<f32>;
+/// @group(#{MATERIAL_BIND_GROUP}) @binding(2) var color_sampler: sampler;
 /// ```
 pub trait Material: Asset + AsBindGroup + Clone + Sized {
     /// Returns this material's vertex shader. If [`ShaderRef::Default`] is returned, the default mesh vertex shader

crates/bevy_render/src/render_resource/bind_group.rs

@@ -133,12 +133,12 @@ impl Deref for BindGroup {
 /// In WGSL shaders, the binding would look like this:
 ///
 /// ```wgsl
-/// @group(3) @binding(0) var<uniform> color: vec4<f32>;
-/// @group(3) @binding(1) var color_texture: texture_2d<f32>;
-/// @group(3) @binding(2) var color_sampler: sampler;
-/// @group(3) @binding(3) var<storage> storage_buffer: array<f32>;
-/// @group(3) @binding(4) var<storage> raw_buffer: array<f32>;
-/// @group(3) @binding(5) var storage_texture: texture_storage_2d<rgba8unorm, read_write>;
+/// @group(#{MATERIAL_BIND_GROUP}) @binding(0) var<uniform> color: vec4<f32>;
+/// @group(#{MATERIAL_BIND_GROUP}) @binding(1) var color_texture: texture_2d<f32>;
+/// @group(#{MATERIAL_BIND_GROUP}) @binding(2) var color_sampler: sampler;
+/// @group(#{MATERIAL_BIND_GROUP}) @binding(3) var<storage> storage_buffer: array<f32>;
+/// @group(#{MATERIAL_BIND_GROUP}) @binding(4) var<storage> raw_buffer: array<f32>;
+/// @group(#{MATERIAL_BIND_GROUP}) @binding(5) var storage_texture: texture_storage_2d<rgba8unorm, read_write>;
 /// ```
 /// Note that the "group" index is determined by the usage context. It is not defined in [`AsBindGroup`]. For example, in Bevy material bind groups
 /// are generally bound to group 2.
@@ -261,7 +261,7 @@ impl Deref for BindGroup {
 ///     roughness: f32,
 /// };
 ///
-/// @group(3) @binding(0) var<uniform> material: CoolMaterial;
+/// @group(#{MATERIAL_BIND_GROUP}) @binding(0) var<uniform> material: CoolMaterial;
 /// ```
 ///
 /// Some less common scenarios will require "struct-level" attributes. These are the currently supported struct-level attributes:
@@ -312,7 +312,7 @@ impl Deref for BindGroup {
 /// declaration:
 ///
 /// ```wgsl
-/// @group(3) @binding(10) var<storage> material_array: binding_array<StandardMaterial>;
+/// @group(#{MATERIAL_BIND_GROUP}) @binding(10) var<storage> material_array: binding_array<StandardMaterial>;
 /// ```
 ///
 /// On the other hand, if you write this declaration:
@@ -325,7 +325,7 @@ impl Deref for BindGroup {
 /// Then Bevy produces a binding that matches this WGSL declaration instead:
 ///
 /// ```wgsl
-/// @group(3) @binding(10) var<storage> material_array: array<StandardMaterial>;
+/// @group(#{MATERIAL_BIND_GROUP}) @binding(10) var<storage> material_array: array<StandardMaterial>;
 /// ```
 ///
 /// * Just as with the structure-level `uniform` attribute, Bevy converts the
@@ -338,7 +338,7 @@ impl Deref for BindGroup {
 ///   this in WGSL in non-bindless mode:
 ///
 /// ```wgsl
-/// @group(3) @binding(0) var<uniform> material: StandardMaterial;
+/// @group(#{MATERIAL_BIND_GROUP}) @binding(0) var<uniform> material: StandardMaterial;
 /// ```
 ///
 /// * For efficiency reasons, `data` is generally preferred over `uniform`

examples/shader_advanced/texture_binding_array.rs

@@ -164,15 +164,15 @@ impl AsBindGroup for BindlessMaterial {
             (
                 // Screen texture
                 //
-                // @group(3) @binding(0) var textures: binding_array<texture_2d<f32>>;
+                // @group(#{MATERIAL_BIND_GROUP}) @binding(0) var textures: binding_array<texture_2d<f32>>;
                 (
                     0,
                     texture_2d(TextureSampleType::Float { filterable: true })
                         .count(NonZero::<u32>::new(MAX_TEXTURE_COUNT as u32).unwrap()),
                 ),
                 // Sampler
                 //
-                // @group(3) @binding(1) var nearest_sampler: sampler;
+                // @group(#{MATERIAL_BIND_GROUP}) @binding(1) var nearest_sampler: sampler;
                 //
                 // Note: as with textures, multiple samplers can also be bound
                 // onto one binding slot: