Disallow array types in var<immediate>

[beicause]

Connections
#8556

Description
Arrays and struct containing array members are disallowed in var<immediate>
https://gpuweb.github.io/gpuweb/wgsl/#ref-for-address-spaces-immediate%E2%91%A0

Testing
cargo xtask cts 'webgpu:shader,validation,decl,immediate:store_type,invalid:*' and cargo test -p naga array_in_immediate

Squash or Rebase?
Squash

Checklist

• I self-reviewed and fully understand this PR.
• WebGPU implementations built with wgpu may be affected behaviorally.
• Validation and feature gates are in place to confine behavioral changes.
• Tests demonstrate the validation and altered logic works.
• CHANGELOG.md entries for the user-facing effects of this change are present.
• The PR is minimal, and doesn't make sense to land as multiple PRs.
• Commits are logically scoped and individually reviewable.
• The PR description has enough context to understand the motivation and solution implemented.