feature #59890 [VarExporter] Leverage native lazy objects (nicolas-grekas)

This PR was merged into the 7.3 branch.

Discussion
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[VarExporter] Leverage native lazy objects

| Q             | A
| ------------- | ---
| Branch?       | 7.3
| Bug fix?      | no
| New feature?  | yes
| Deprecations? | no
| Issues        | -
| License       | MIT

Let's leverage native lazy objects.

Instead of keeping/updating LazyGhostTrait and LazyProxyTrait, I'm deprecating them in favor of using native lazy proxies directly.

There is one use case that is not covered by native lazy objects: lazy decorators - aka lazy proxies built against an interface or an internal class. For this use case, we keep `ProxyHelper::generateLazyProxy()`.

Commits
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a00855a4934 [VarExporter] Leverage native lazy objects

Author: nicolas-grekas

Tests/Security/User/EntityUserProviderTest.php

@@ -136,6 +136,9 @@ public function testRefreshInvalidUser()
         $provider->refreshUser($user2);
     }
 
+    /**
+     * @group legacy
+     */
     public function testSupportProxy()
     {
         $em = DoctrineTestHelper::createTestEntityManager();
@@ -202,6 +205,9 @@ public function testPasswordUpgrades()
         $provider->upgradePassword($user, 'foobar');
     }
 
+    /**
+     * @group legacy
+     */
     public function testRefreshedUserProxyIsLoaded()
     {
         $em = DoctrineTestHelper::createTestEntityManager();

Tests/Validator/Constraints/UniqueEntityValidatorTest.php

@@ -223,6 +223,9 @@ public static function provideUniquenessConstraints(): iterable
         yield 'Named arguments' => [new UniqueEntity(message: 'myMessage', fields: ['name'], em: 'foo')];
     }
 
+    /**
+     * @group legacy
+     */
     public function testValidateEntityWithPrivatePropertyAndProxyObject()
     {
         $entity = new SingleIntIdWithPrivateNameEntity(1, 'Foo');