Avoid cached expression recursion during loop narrowing

[Copilot]

Control flow analysis could stack overflow when narrowing a loop variable assigned from an as const object that references the same variable. The cached expression path discarded in-progress loop-flow state, preventing recursive loop analysis from terminating.

Example:

let lastCandidate: Candidate | null = null;
while (true) {
    const candidate: Candidate = {
        mode: "a",
        output: lastCandidate,
    } as const;
    lastCandidate = candidate;
}

• Flow analysis

  • Avoids expression caching while loop flow analysis is already in progress.
  • Preserves the active loop-flow stack so recursive references can use incomplete loop types instead of restarting uncached analysis.

• Tests

  • Adds a compiler regression test for the as const loop assignment crash.
  • Updates affected loop narrowing baselines where precise types are now retained instead of circular any errors.

• Fixes Stack overflow narrowing as const object assigned to loop variable it references #64012