Squiz/StaticThisUsage: always skip nested anonymous scope

As things were, the `Squiz.Scope.StaticThisUsage` sniff already skipped over the body of anonymous classes when found within the body of a static OO method, to prevent false positives related to `$this` when it refers to the anonymous class.
However, the sniff did not skip over the body of an anonymous function (closure).

This is wrong, as anonymous functions can be bound to an object, in which case the closure has access to that object via `$this`.
However, whether the object is actually bound or not, is irrelevant. The closure has its own (closed) scope and doesn't have access to variables from outside the closure, so any usages of `$this` _within_ the closure would not be the "static this usage" this sniff is looking for anyway.

With that in mind, the sniff should skip over the body of closures, same as it skips over the body of anonymous classes.

Having said that, I also believe that the sniff should explicitly examine `static` closures for the use of `$this`, while it currently doesn't (false negative), but that's another matter.

Fixes 1357

Related to previous iterations:
* squizlabs/PHP_CodeSniffer 1747 - solved via 8ad3826
* squizlabs/PHP_CodeSniffer 2725

Author: jrfnl

src/Standards/Squiz/Sniffs/Scope/StaticThisUsageSniff.php

@@ -86,12 +86,15 @@ private function checkThisUsage(File $phpcsFile, int $next, int $end)
         $tokens = $phpcsFile->getTokens();
 
         do {
-            $next = $phpcsFile->findNext([T_VARIABLE, T_ANON_CLASS], ($next + 1), $end);
+            $next = $phpcsFile->findNext([T_VARIABLE, T_CLOSURE, T_ANON_CLASS], ($next + 1), $end);
             if ($next === false) {
                 continue;
             }
 
-            if ($tokens[$next]['code'] === T_ANON_CLASS) {
+            if (($tokens[$next]['code'] === T_ANON_CLASS
+                || $tokens[$next]['code'] === T_CLOSURE)
+                && isset($tokens[$next]['scope_opener']) === true
+            ) {
                 $this->checkThisUsage($phpcsFile, $next, $tokens[$next]['scope_opener']);
                 $next = $tokens[$next]['scope_closer'];
                 continue;

src/Standards/Squiz/Tests/Scope/StaticThisUsageUnitTest.inc

@@ -125,3 +125,22 @@ enum MyEnum {
         $this->doSomething();
     }
 }
+
+class NestedScopesShouldBeSkipped
+{
+    public static function examineMe() {
+        $this->shouldBeFlagged();
+
+        function nestedFunction() {
+            $this->nestedFunctionsDoNotHaveAccessToThis();
+        }
+
+        \Closure::bind(
+            function ($this) { // Cannot use $this as a param, so this should still be flagged.
+                $this->x = 1; // This is fine. $this related to the Closure class, not to the NestedScopesShouldBeSkipped class.
+            },
+            new Target(),
+            Target::class,
+        )();
+    }
+}

src/Standards/Squiz/Tests/Scope/StaticThisUsageUnitTest.php

@@ -37,14 +37,16 @@ public function getErrorList()
             9   => 1,
             14  => 1,
             20  => 1,
-            41  => 1,
             61  => 1,
             69  => 1,
             76  => 1,
             80  => 1,
             84  => 1,
             99  => 1,
             125 => 1,
+            132 => 1,
+            135 => 1,
+            139 => 1,
         ];
     }