Ensure gtInitializeStoreNode consistently handles SIMD/Mask stores for all platforms

[tannergooding]

This was consistent for everything except x86 and we weren't handling masks as intended for x64.

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[Copilot]

Pull request overview

This PR updates Compiler::gtInitializeStoreNode so that SIMD and mask local stores are consistently marked as “related to SIMD intrinsics” across all target platforms, eliminating the prior x86-only special-case and extending the behavior to mask stores (when enabled).

Changes:

• Replace the x86-only heuristic with a single all-arch path.
• Detect SIMD/mask stores via varTypeIsSIMDOrMask(store) and apply SetOpLclRelatedToSIMDIntrinsic consistently to both the store node and the stored value (preserving the existing retbuf-call exclusion).

[tannergooding]

CC. @jakobbotsch, @EgorBo. Minor code cleanup to ensure x86 (32-bit) is consistent with other SIMD platforms, removes an ifdef.

Provides minor improvements to x86 fullopts:

Overall (-3,868 bytes)
FullOpts (-3,868 bytes)
Example diffs

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated no new comments.

[tannergooding]

/ba-g unrelated timeouts