Squiz/ClassFileName: don't error when there is no class name

As things were, the sniff would try to find the next `T_STRING`, but didn't take live coding into account, which means it would end up comparing `$tokens[false]['content']` to the filename, which would end up comparing `<?php` to the file name.

This changes the sniff to use the `File::getDeclarationName()` method instead and verifies we have a usable name to compare against before throwing the error.

Includes test.

Author: jrfnl

src/Standards/Squiz/Sniffs/Classes/ClassFileNameSniff.php

@@ -51,10 +51,14 @@ public function process(File $phpcsFile, $stackPtr)
         $fullPath = basename($filename);
         $fileName = substr($fullPath, 0, strrpos($fullPath, '.'));
 
-        $tokens  = $phpcsFile->getTokens();
-        $decName = $phpcsFile->findNext(T_STRING, $stackPtr);
+        $tokens = $phpcsFile->getTokens();
+        $ooName = $phpcsFile->getDeclarationName($stackPtr);
+        if ($ooName === null) {
+            // Probably parse error/live coding.
+            return;
+        }
 
-        if ($tokens[$decName]['content'] !== $fileName) {
+        if ($ooName !== $fileName) {
             $error = '%s name doesn\'t match filename; expected "%s %s"';
             $data  = [
                 ucfirst($tokens[$stackPtr]['content']),

src/Standards/Squiz/Tests/Classes/ClassFileNameParseError1UnitTest.inc

@@ -0,0 +1,6 @@
+<?php
+
+// Intentional parse error. This should be the only test in this file.
+// Class missing class name should be ignored.
+
+class