Fix panic when using globals uniform in wasm builds (#6460)

# Objective

Fixes #5393 

## Solution

- Add padding to `GlobalsUniform` / `Globals` to make it 16-byte aligned.

Still not super clear on whether this is a `naga` thing or an `encase` thing or what. But now that we're offering `globals` up to users and #5393 is not just breaking an example, maybe we should do this sort of workaround?

crates/bevy_pbr/src/render/mesh_view_types.wgsl

@@ -95,4 +95,8 @@ struct Globals {
     // Frame count since the start of the app.
     // It wraps to zero when it reaches the maximum value of a u32.
     frame_count: u32,
+#ifdef SIXTEEN_BYTE_ALIGNMENT
+    // WebGL2 structs must be 16 byte aligned.
+    _wasm_padding: f32
+#endif
 }

crates/bevy_render/src/globals.rs

@@ -41,6 +41,9 @@ pub struct GlobalsUniform {
     /// Frame count since the start of the app.
     /// It wraps to zero when it reaches the maximum value of a u32.
     frame_count: u32,
+    /// WebGL2 structs must be 16 byte aligned.
+    #[cfg(feature = "webgl")]
+    _wasm_padding: f32,
 }
 
 /// The buffer containing the [`GlobalsUniform`]

crates/bevy_render/src/render_resource/pipeline_cache.rs

@@ -151,7 +151,10 @@ impl ShaderCache {
             Entry::Vacant(entry) => {
                 let mut shader_defs = shader_defs.to_vec();
                 #[cfg(feature = "webgl")]
-                shader_defs.push(String::from("NO_ARRAY_TEXTURES_SUPPORT"));
+                {
+                    shader_defs.push(String::from("NO_ARRAY_TEXTURES_SUPPORT"));
+                    shader_defs.push(String::from("SIXTEEN_BYTE_ALIGNMENT"));
+                }
 
                 // TODO: 3 is the value from CLUSTERED_FORWARD_STORAGE_BUFFER_COUNT declared in bevy_pbr
                 // consider exposing this in shaders in a more generally useful way, such as: