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/Fixtures/LazyResettableService.php

@@ -11,7 +11,7 @@
 
 namespace Symfony\Component\HttpKernel\Tests\Fixtures;
 
-class LazyResettableService
+class LazyResettableService extends \stdClass
 {
     public static $counter = 0;