PHP namespaces for nested messages and enums (#4536)

* uses namespaces for nested messages and enums

* fixes namespaces for PHP dist

* fixes namespace for Descriptors, adds Cardinality and Kind

* fixes nested namespaces for reserved words and adds tests

* adds tests and generator fix for php class prefixes

* fixes escaping of protobuf packages, enum comments, misc others

* nice refactor of generated code

* adds class files for backwards compatibility

* simplifies code with templates

* adds compatibility files to makefile

* cleanup of generator and fixes nested namespace bug

* regenerates proto types

* remove internal BC classes

* adds deprecated warning, adds methods back

* simplifies if statement

* fixes dist files

* addresses review comments

* adds back TYPE_URL_PREFIX constant

* adds @deprecated to old nested class files

* skips tests which require a separate process when protobuf.so is enabled

* Adds tests for legacy nested classes that do not require separate processes to test

* uses legacy names for GPBUtil message check

* adds block for IDE @deprecated message

* Namespace for nested message/enum in c extension

* Remove unused code

php/tests/array_test.php

diff --git a/php/tests/array_test.php b/php/tests/array_test.php
index 1a26d72..36a649e 100644
--- a/php/tests/array_test.php
+++ b/php/tests/array_test.php
@@ -5,7 +5,7 @@
 use Google\Protobuf\Internal\RepeatedField;
 use Google\Protobuf\Internal\GPBType;
 use Foo\TestMessage;
-use Foo\TestMessage_Sub;
+use Foo\TestMessage\Sub;
 
 class RepeatedFieldTest extends PHPUnit_Framework_TestCase
 {
@@ -456,10 +456,10 @@
 
     public function testMessage()
     {
-        $arr = new RepeatedField(GPBType::MESSAGE, TestMessage_Sub::class);
+        $arr = new RepeatedField(GPBType::MESSAGE, Sub::class);
 
         // Test append.
-        $sub_m = new TestMessage_Sub();
+        $sub_m = new Sub();
         $sub_m->setA(1);
         $arr[] = $sub_m;
         $this->assertSame(1, $arr[0]->getA());
@@ -467,15 +467,15 @@
         $this->assertEquals(1, count($arr));
 
         // Test set.
-        $sub_m = new TestMessage_Sub();
+        $sub_m = new Sub();
         $sub_m->setA(2);
         $arr[0] = $sub_m;
         $this->assertSame(2, $arr[0]->getA());
 
         // Test foreach.
-        $arr = new RepeatedField(GPBType::MESSAGE, TestMessage_Sub::class);
+        $arr = new RepeatedField(GPBType::MESSAGE, Sub::class);
         for ($i = 0; $i < 3; $i++) {
-          $arr[] = new TestMessage_Sub();
+          $arr[] = new Sub();
           $arr[$i]->setA($i);
         }
         $i = 0;