[php-nextgen] add php-nextgen client generator (#16480)

* php-nextgen first commit

* [php] Set minimal PHP version to ^8.0 (#14500)

* Set minimal PHP version to ^8.0

* Fix php-nextgen config

* Change stability to BETA

* Add phplint package (#15054)

* [php-nextgen] Rename folders to follow PDS skeleton (#15102)

* Change lib -> src, test -> tests folder

This will make build compliant to PHP-PDS skeleton.
Ref: https://github.com/php-pds/skeleton

* Refresh samples

* Exclude composer.lock from codebase (#15105)

Since client generator is library and not a project it makes sense
to exclude composer.lock from codebase by default.

Ref: http://getcomposer.org/doc/02-libraries.md#lock-file

* Add @generated tag to DocBlocks (#15106)

This tag in draft status right now(PSR-19), but I think we can leverage
from it already.

Ref: https://github.com/php-fig/fig-standards/blob/master/proposed/phpdoc-tags.md#55-generated

* update samples, doc

* update samples

---------

Co-authored-by: Yuriy Belenko <yura-bely@mail.ru>

samples/client/petstore/php-nextgen/OpenAPIClient-php/test/ModelInheritanceTest.php

@@ -0,0 +1,96 @@
+<?php
+
+namespace OpenAPI\Client;
+
+use OpenAPI\Client\Model\Animal;
+use OpenAPI\Client\Model\Cat;
+use OpenAPI\Client\Model\Dog;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Test that Dog properly inherit Animal
+ *
+ * @package OpenAPI\Client
+ */
+class ModelInheritanceTest extends TestCase
+{
+    /**
+     * test if default values works
+     */
+    public function testDefaultValues()
+    {
+        // add some animals to the farm to make sure the ArrayAccess
+        // interface works
+        $dog = new Dog();
+        $animal = new Animal();
+
+        // assert we can look up the animals in the farm by array
+        // indices (let's try a random order)
+        $this->assertSame('red', $dog->getColor());
+        $this->assertSame('red', $animal->getColor());
+    }
+
+    /**
+     * test inheritance in the model
+     */
+    public function testInheritance()
+    {
+        $newDog = new Dog;
+        // the object should be an instance of the derived class
+        $this->assertInstanceOf(Dog::class, $newDog);
+        // the object should also be an instance of the parent class
+        $this->assertInstanceOf(Animal::class, $newDog);
+    }
+
+    /**
+     * test inheritance constructor is working with data initialization
+     */
+    public function testInheritanceConstructorDataInitialization()
+    {
+        // initialize the object with data in the constructor
+        $data = [
+            'class_name' => 'Dog',
+            'breed' => 'Great Dane',
+        ];
+        $newDog = new Dog($data);
+
+        // the property on the derived class should be set
+        $this->assertSame('Great Dane', $newDog->getBreed());
+        // the property on the parent class should be set
+        $this->assertSame('Dog', $newDog->getClassName());
+    }
+
+    /**
+     * test if discriminator is initialized automatically
+     */
+    public function testDiscriminatorInitialization()
+    {
+        $newDog = new Dog();
+        $this->assertSame('Dog', $newDog->getClassName());
+    }
+
+    /**
+     * test if ArrayAccess interface works
+     */
+    public function testArrayStuff()
+    {
+        // create an array of Animal
+        $farm = array();
+
+        // add some animals to the farm to make sure the ArrayAccess interface works
+        $farm[] = new Dog();
+        $farm[] = new Cat();
+        $farm[] = new Animal();
+
+        // assert we can look up the animals in the farm by array indices (let's try a random order)
+        $this->assertInstanceOf(Cat::class, $farm[1]);
+        $this->assertInstanceOf(Dog::class, $farm[0]);
+        $this->assertInstanceOf(Animal::class, $farm[2]);
+
+        // let's try to `foreach` the animals in the farm and let's try to use the objects we loop through
+        foreach ($farm as $animal) {
+            $this->assertContains($animal->getClassName(), ['Dog', 'Cat', 'Animal']);
+            $this->assertInstanceOf('OpenAPI\Client\Model\Animal', $animal);
+        }
+    }
+}