[compiler] Allow ref initialization with sentinel values

[trandaiviethung2001]

Summary

Fixes #30782.

Allow the ref access validator to recognize lazy initialization patterns that use a module-level sentinel value passed to useRef, for example useRef(UNINITIALIZED) guarded by ref.current === UNINITIALIZED.

The validator now tracks a stable key for non-local bindings so repeated LoadGlobal(module) reads of the same sentinel compare as the same initial value. It preserves the existing nullish initialization behavior and keeps non-null arbitrary initialization patterns rejected.

How did you test this change?

• corepack yarn workspace snap run build
• corepack yarn workspace snap run snap --pattern allow-ref-initialization-symbol --sync
• corepack yarn workspace snap run snap --pattern allow-ref-initialization --sync
• corepack yarn workspace snap run snap --pattern error.ref-initialization-arbitrary --sync
• corepack yarn workspace snap run snap --pattern error.ref-initialization-other --sync
• corepack yarn workspace snap run snap --pattern error.ref-initialization-linear --sync

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