minor #19565 Make IDEs handle the configuration tree (leofeyer)

This PR was submitted for the 2.8 branch but it was merged into the 2.7 branch instead (closes #19565).

Discussion
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Make IDEs handle the configuration tree

| Q             | A
| ------------- | ---
| Branch?       | 2.7
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

When defining a configuration tree, my IDE (PhpStorm) gives me a lot of `Method 'scalarNode' not found in null|\Symfony\Component\Config\Definition\Builder\NodeParentInterface` warnings. This can easily be fixed by adding more return types to the phpDoc comments of the `end()` methods of the `NodeBuilder` and `NodeDefinition` classes.

Commits
-------

4e8bfc6 Enhance the phpDoc return types so IDEs can handle the configuration tree.

src/Symfony/Component/Config/Definition/Builder/NodeBuilder.php

@@ -138,7 +138,7 @@ class NodeBuilder implements NodeParentInterface
     /**
      * Returns the parent node.
      *
-     * @return ParentNodeDefinitionInterface The parent node
+     * @return ParentNodeDefinitionInterface|NodeDefinition The parent node
      */
     public function end()
     {

src/Symfony/Component/Config/Definition/Builder/NodeDefinition.php

@@ -107,7 +107,7 @@ abstract class NodeDefinition implements NodeParentInterface
     /**
      * Returns the parent node.
      *
-     * @return NodeParentInterface|null The builder of the parent node
+     * @return NodeParentInterface|NodeBuilder|NodeDefinition|null The builder of the parent node
      */
     public function end()
     {