Repro for false positive in validatePreserveMemoization on non-escaping value

This demonstrates a false positive in validatePreserveExistingManualMemoization. 
We prune memoization of non-escaping values, but the validation pass just sees 
that the value "should" have a scope and that scope doesn't exist, and thinks we 
failed to preserve memoization.

compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/error.repro-false-positive-preserve-memoization-nonescaping-value.expect.md

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+
+## Input
+
+```javascript
+// @validatePreserveExistingMemoizationGuarantees @enableAssumeHooksFollowRulesOfReact @enableTransitivelyFreezeFunctionExpressions
+function Component({ entity, children }) {
+  // showMessage doesn't escape so we don't memoize it.
+  // However, validatePreserveExistingMemoizationGuarantees only sees that the scope
+  // doesn't exist, and thinks the memoization was missed instead of being intentionally dropped.
+  const showMessage = useCallback(() => entity != null);
+
+  if (!showMessage) {
+    return children;
+  }
+
+  return <Message>{children}</Message>;
+}
+
+```
+
+
+## Error
+
+```
+[ReactForget] InvalidReact: This value was manually memoized, but cannot be memoized under Forget because it may be mutated after it is memoized (6:6)
+```
+          
+      

compiler/packages/babel-plugin-react-forget/src/__tests__/fixtures/compiler/error.repro-false-positive-preserve-memoization-nonescaping-value.js

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+// @validatePreserveExistingMemoizationGuarantees @enableAssumeHooksFollowRulesOfReact @enableTransitivelyFreezeFunctionExpressions
+function Component({ entity, children }) {
+  // showMessage doesn't escape so we don't memoize it.
+  // However, validatePreserveExistingMemoizationGuarantees only sees that the scope
+  // doesn't exist, and thinks the memoization was missed instead of being intentionally dropped.
+  const showMessage = useCallback(() => entity != null);
+
+  if (!showMessage) {
+    return children;
+  }
+
+  return <Message>{children}</Message>;
+}