[naga] Add packed as a keyword for GLSL

Turns out that sometimes `packed` is a keyword,
and the produced GLSL had syntax errors due to that.

CHANGELOG.md

@@ -181,6 +181,7 @@ By @atlv24 in [#5383](https://github.com/gfx-rs/wgpu/pull/5383)
 #### Naga
 
 - In spv-out don't decorate a `BindingArray`'s type with `Block` if the type is a struct with a runtime array by @Vecvec in [#5776](https://github.com/gfx-rs/wgpu/pull/5776)
+- Add `packed` as a keyword for GLSL by @kjarosh in [#5855](https://github.com/gfx-rs/wgpu/pull/5855)
 
 ## v0.20.0 (2024-04-28)
 

naga/src/back/glsl/keywords.rs

@@ -473,6 +473,8 @@ pub const RESERVED_KEYWORDS: &[&str] = &[
     "anyInvocation",
     "allInvocations",
     "allInvocationsEqual",
+    // Sometimes "packed" is a keyword, see https://github.com/gfx-rs/wgpu/issues/5853
+    "packed",
     //
     // entry point name (should not be shadowed)
     //