chore(cdk-build-tools): backport feature flag based conditional from …

…v2-main (#13056)

This was originally commented out - d7e028a - since this was not yet
compatible with the v2-main branch.

Since then, the v2-main branch has been updated - 7554246 - with the
necessary fixes and the conditional has been enabled there[1].

No effective change to master branch because of this. It reduces divergence
of the two active branches.

[1]: 7554246#diff-d325e066c7cdf5d2a8423e65b0190045defe711b4dc25adc0a94a11eef163ed9


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*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

tools/cdk-build-tools/lib/feature-flag.ts

@@ -30,9 +30,8 @@ export function testFutureBehavior<T>(
 
   const major = cdkMajorVersion(repoRoot);
   if (major === 2) {
-    // Temporaily disable CDKv2 behaviour
-    // const app = new cdkApp();
-    // return test(name, async () => fn(app));
+    const app = new cdkApp();
+    return test(name, async () => fn(app));
   }
   const app = new cdkApp({ context: flags });
   return test(name, () => fn(app));
@@ -59,8 +58,7 @@ export function testLegacyBehavior<T>(
 
   const major = cdkMajorVersion(repoRoot);
   if (major === 2) {
-    // Temporarily disable CDKv2 behaviour
-    // return;
+    return;
   }
   const app = new cdkApp();
   return test(name, () => fn(app));
@@ -78,4 +76,4 @@ function cdkMajorVersion(repoRoot: string) {
     throw new Error(`version ${ver} is not a semver`);
   }
   return sem.major;
-}
+}