bug #61728 [TypeInfo] Fix issue with merging union type with a nullable union type (matijn-made)

This PR was merged into the 7.3 branch.

Discussion
----------

[TypeInfo] Fix issue with merging union type with a nullable union type

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

The new TypeInfo component doesn't handle this situation correctly.
Found this after upgrading to 7.3, where the PropertyInfo now calls TypeInfo, given this docblock:
```php
/**
 * `@phpstan`-type NullableUnionType = string|int|null
 * `@phpstan`-type UnionWithNullableUnionType = float|NullableUnionType
 */
```

In 7.3 it will throw `Symfony\Component\TypeInfo\Exception\InvalidArgumentException: Cannot set "Symfony\Component\TypeInfo\Type\UnionType" as a "Symfony\Component\TypeInfo\Type\UnionType" part.` exception.
This PR makes sure that nullable union types are also merged, before being passed to a new UnionType

Commits
-------

3f4e4228fd6 Fix issue with merging union type with a nullable union type

Author: nicolas-grekas

Tests/TypeFactoryTest.php

@@ -204,6 +204,10 @@ public function testCreateNullable()
             new NullableType(new UnionType(new BuiltinType(TypeIdentifier::INT), new BuiltinType(TypeIdentifier::STRING))),
             Type::union(Type::nullable(Type::int()), Type::string()),
         );
+        $this->assertEquals(
+            new NullableType(new UnionType(new BuiltinType(TypeIdentifier::INT), new BuiltinType(TypeIdentifier::STRING))),
+            Type::union(Type::nullable(Type::union(Type::int(), Type::string())), Type::string()),
+        );
     }
 
     public function testCreateArrayShape()

TypeFactoryTrait.php

@@ -299,9 +299,7 @@ public static function union(Type ...$types): UnionType
         foreach ($types as $type) {
             if ($type instanceof NullableType) {
                 $nullableUnion = true;
-                $unionTypes[] = $type->getWrappedType();
-
-                continue;
+                $type = $type->getWrappedType();
             }
 
             if ($type instanceof UnionType) {