Generic/ByteOrderMark: improve test coverage

This commit adds four more tests case files:
* 2 to cover the cases where the sniff is triggered but the file does not contain a BOM character.
    One of these files is in UTF-8 encoding without a BOM, the other is in ANSI/iso-8859-1 encoding.
* 2 to cover the different UTF-16 encodings with a BOM character.

Includes adding a comment to the original test case file to document the encoding (UTF-8 with BOM) of that file.

src/Standards/Generic/Tests/Files/ByteOrderMarkUnitTest.1.inc

@@ -1,3 +1,4 @@
-<?php
-echo 'foo';
-?>
+<?php
+// File in UTF-8 encoding with byte order mark (BOM) character before the opening PHP tag.
+echo 'foo';
+?>

src/Standards/Generic/Tests/Files/ByteOrderMarkUnitTest.2.inc

@@ -0,0 +1,3 @@
+<?php // File in UTF-8 encoding without a byte order mark (BOM) character before the opening PHP tag. ?>
+
+<p>Some HTML</p>

src/Standards/Generic/Tests/Files/ByteOrderMarkUnitTest.3.inc

@@ -0,0 +1 @@
+<p>Some HTML at the beginning of an ANSI/iso-8859-1 encoded file without a byte order mark (BOM) character</p>

src/Standards/Generic/Tests/Files/ByteOrderMarkUnitTest.php

@@ -34,6 +34,8 @@ public function getErrorList($testFile='')
     {
         switch ($testFile) {
         case 'ByteOrderMarkUnitTest.1.inc':
+        case 'ByteOrderMarkUnitTest.4.inc':
+        case 'ByteOrderMarkUnitTest.5.inc':
             return [1 => 1];
 
         default: