Extra WGSL validation for @align

[alan-baker]

• Cover no value decl usage
• Cover more address spaces
• Cover other types of decls

Issue: #

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Requirements for PR author:

• All missing test coverage is tracked with "TODO" or .unimplemented().
• New helpers are /** documented */ and new helper files are found in helper_index.txt.
• Test behaves as expected in a WebGPU implementation. (If not passing, explain above.)
• Test have be tested with compatibility mode validation enabled and behave as expected. (If not passing, explain above.)

Requirements for reviewer sign-off:

• Tests are properly located.
• Test descriptions are accurate and complete.
• Tests provide complete coverage (including validation control cases). Missing coverage MUST be covered by TODOs.
• Tests avoid over-parameterization (see case count report).

When landing this PR, be sure to make any necessary issue status updates.

[github-actions]

Results for build job (at 4db18d6):

-webgpu:shader,validation,shader_io,align:required_alignment:* - 256 cases, 256 subcases (~1/case)
+webgpu:shader,validation,shader_io,align:required_alignment:* - 36 cases, 1128 subcases (~31/case)
-TOTAL: 283229 cases, 2325040 subcases
+TOTAL: 283009 cases, 2325912 subcases