Pointer aliasing

[alan-baker]

TODO: uniformity test updates

Issue: #

---

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 f81c6b1):

+webgpu:shader,execution,expression,call,user,ptr_aliasing:two_pointers:* - 24 cases, 312 subcases (~13/case)
+webgpu:shader,execution,expression,call,user,ptr_aliasing:two_pointers_dynamic_index:* - 8 cases, 104 subcases (~13/case)
+webgpu:shader,execution,expression,call,user,ptr_aliasing:composite_and_element:* - 16 cases, 80 subcases (~5/case)
+webgpu:shader,execution,expression,call,user,ptr_aliasing:composite_copy:* - 16 cases, 48 subcases (~3/case)
+webgpu:shader,execution,expression,call,user,ptr_aliasing:one_pointer_one_module_scope:* - 18 cases, 90 subcases (~5/case)
+webgpu:shader,execution,expression,call,user,ptr_aliasing:two_atomic_pointers:* - 8 cases, 24 subcases (~3/case)
+webgpu:shader,execution,expression,call,user,ptr_aliasing:loop_carried_dependence:* - 8 cases, 32 subcases (~4/case)
+webgpu:shader,execution,expression,call,user,ptr_aliasing:buffer_view_mixed_types:* - 1458 cases, 7290 subcases (~5/case)
+webgpu:shader,validation,functions,alias_analysis:requires_unrestricted_aliasing:* - 8 cases, 8 subcases (~1/case)
-webgpu:shader,validation,parse,requires:wgsl_matches_api:* - 14 cases, 14 subcases (~1/case)
-webgpu:shader,validation,parse,requires:have_all_language_features:* - 14 cases, 14 subcases (~1/case)
+webgpu:shader,validation,parse,requires:wgsl_matches_api:* - 15 cases, 15 subcases (~1/case)
+webgpu:shader,validation,parse,requires:have_all_language_features:* - 15 cases, 15 subcases (~1/case)
-TOTAL: 287982 cases, 2362149 subcases
+TOTAL: 289548 cases, 2370139 subcases