feature #4355 GlobalNamespaceImportFixer - Introduction (gharlan)

This PR was squashed before being merged into the 2.16-dev branch (closes #4355).

Discussion
----------

GlobalNamespaceImportFixer - Introduction

* closes #1309
* refs #2166 (this pr does not differientiate between native/non-native elements, only between global/non-global)
* closes #2739
* closes #4347

---

The fixer can import global classes/functions/constants:

Input:

```php
<?php

namespace Foo;

if (\count($x)) {
    /** @var \DateTimeImmutable $d */
    $d = new \DateTimeImmutable();
    $p = \M_PI;
}
```

Output:

```php
<?php

namespace Foo;
use DateTimeImmutable;
use function count;
use const M_PI;

if (count($x)) {
    /** @var DateTimeImmutable $d */
    $d = new DateTimeImmutable();
    $p = M_PI;
}
```

Global functions/constants without leading `\` are not imported. The slash can be added by `Native(Constant|Function)InvocationFixer` before.

The fixer can also do the reverse fix, adding the backslash to imported global classes/functions/constants. But the fixer does not remove the imports, this can be done by `NoUnusedImportsFixer`.

Commits
-------

41fe1f4 GlobalNamespaceImportFixer - Introduction

README.rst

@@ -743,6 +743,19 @@ Choose from the list of available rules:
   - ``annotations`` (``array``): list of annotations to remove, e.g. ``["author"]``;
     defaults to ``[]``
 
+* **global_namespace_import**
+
+  Imports or fully qualifies global classes/functions/constants.
+
+  Configuration options:
+
+  - ``import_classes`` (``false``, ``null``, ``true``): whether to import, not import or
+    ignore global classes; defaults to ``true``
+  - ``import_constants`` (``false``, ``null``, ``true``): whether to import, not import or
+    ignore global constants; defaults to ``null``
+  - ``import_functions`` (``false``, ``null``, ``true``): whether to import, not import or
+    ignore global functions; defaults to ``null``
+
 * **hash_to_slash_comment**
 
   Single line comments should use double slashes ``//`` and not hash ``#``.

src/Fixer/ConstantNotation/NativeConstantInvocationFixer.php

@@ -92,6 +92,15 @@ public function getDefinition()
         );
     }
 
+    /**
+     * {@inheritdoc}
+     */
+    public function getPriority()
+    {
+        // must be run before GlobalNamespaceImportFixer
+        return 10;
+    }
+
     /**
      * {@inheritdoc}
      */

src/Fixer/FunctionNotation/NativeFunctionInvocationFixer.php

@@ -160,6 +160,15 @@ function baz($options)
         );
     }
 
+    /**
+     * {@inheritdoc}
+     */
+    public function getPriority()
+    {
+        // must be run before GlobalNamespaceImportFixer
+        return 10;
+    }
+
     /**
      * {@inheritdoc}
      */