Add CFA regression test for while loop with continue statements

[Copilot]

This PR adds a regression test for Control Flow Analysis (CFA) behavior in while loops with continue statements, addressing issue #987.

The test captures a specific scenario where our TypeScript Go implementation's control flow analysis needed to correctly track variable nullability through while loops containing continue statements:

class A {
  next: A | null = null;
  constructor(readonly children: (A | null)[]) {}
}

function getNodes(): A[] {
  const out: A[] = [];
  let current: A | null = new A([]);

  while (current !== null) {
    let firstChild = null;

    // Critical CFA test case: continue statement after null check
    if (out.length) {
      current = current.next;
      continue;
    }

    // After the continue, current should still be known to be non-null
    for (let i = 0; i < current.children.length; i++) {
      const child = current.children[i];
      if (child) {
        if (!firstChild) {
          firstChild = child;
          firstChild.next = current.next;
        }
        child.next = current.next;
      }
    }

    current = firstChild || current.next;
  }

  return out;
}

The test verifies that:

• After the while (current !== null) condition, current is correctly narrowed from A | null to A
• This narrowing is preserved through the continue statement
• All subsequent references to current within the loop body recognize it as non-null

The generated baselines confirm that our CFA implementation correctly handles this complex control flow pattern, ensuring consistency with the stable TypeScript compiler behavior.

Fixes #1324.

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