Adds PHP 7.4 fn closure surrpot in PSR12.Functions.ReturnTypeDeclaration

Author: michalbundyra

src/Standards/PSR12/Sniffs/Functions/ReturnTypeDeclarationSniff.php

@@ -27,6 +27,7 @@ public function register()
         return [
             T_FUNCTION,
             T_CLOSURE,
+            T_FN,
         ];
 
     }//end register()

src/Standards/PSR12/Tests/Functions/ReturnTypeDeclarationUnitTest.inc

@@ -60,3 +60,5 @@ function functionName(?string $arg1, ?int &$arg2):?string {}
 function functionName(?string $arg1, ?int &$arg2):  ?string {}
 function functionName(?string $arg1, ?int &$arg2):
 ?string {}
+
+fn (?\DateTime $arg) : ?\DateTime => $arg;

src/Standards/PSR12/Tests/Functions/ReturnTypeDeclarationUnitTest.inc.fixed

@@ -56,3 +56,5 @@ function functionName(?string $arg1, ?int &$arg2): ?string {}
 function functionName(?string $arg1, ?int &$arg2): ?string {}
 function functionName(?string $arg1, ?int &$arg2): ?string {}
 function functionName(?string $arg1, ?int &$arg2): ?string {}
+
+fn (?\DateTime $arg): ?\DateTime => $arg;

src/Standards/PSR12/Tests/Functions/ReturnTypeDeclarationUnitTest.php

@@ -37,6 +37,7 @@ protected function getErrorList()
             59 => 1,
             60 => 1,
             62 => 1,
+            64 => 1,
         ];
 
     }//end getErrorList()