React Compiler migration: foundation (validate against compiled output)

[mattcosta7]

Closes #

React Compiler migration — foundation

Groundwork so we can migrate the remaining components onto the React Compiler and validate them against compiled output.

What this does

1. REACT_COMPILER_ALL=true opt-in in isSupported: compiles all (non-test) source files, so the full test suite can be run against compiled output to validate a bulk migration (REACT_COMPILER_ALL=true npm test).
2. Never compile *.test.* / *.stories.* files. The compiler injects hooks (_c/useMemo) into ad-hoc test/story helper components, which throw "Invalid hook call". Excluding them also means migrating a component won't break its own test file. (This fixed spurious ActionMenu/SelectPanel/TooltipV2 failures in validation.)
3. Remove the dead react-compiler/react-compiler ESLint override (and its now-unused import). That plugin isn't installed; as of eslint-plugin-react-hooks@7.1.1 the compiler diagnostics are the granular react-hooks/* rules (set-state-in-effect, immutability, refs, purity, …), already enabled repo-wide by recommended-latest. The old override was a silent no-op.

Validation

Ran REACT_COMPILER_ALL=true across the full browser suite: 2016/2016 behavioral tests pass compiled (the only failures are pre-existing CSS-module-hash snapshot mismatches unrelated to the compiler — tracked separately).

Rollout

• None (build/test tooling only; no consumer-facing change)

Merge checklist

• Added/updated tests (validation harness)
• Changes are SSR compatible

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Latest commit: 1609573

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