Tests/HeredocNowdocCloserTest: use named data sets

With non-named data sets, when a test fails, PHPUnit will display the number of the test which failed.

With tests which have a _lot_ of data sets, this makes it _interesting_ (and time-consuming) to debug those, as one now has to figure out which of the data sets in the data provider corresponds to that number.

Using named data sets makes debugging failing tests more straight forward as PHPUnit will display the data set name instead of the number.
Using named data sets also documents what exactly each data set is testing.

Includes making the data type in the docblock more specific.
Includes fixing up the docblock description for the file.

tests/Core/Tokenizer/HeredocNowdocCloserTest.php

@@ -1,6 +1,6 @@
 <?php
 /**
- * Tests the tokenization of goto declarations and statements.
+ * Tests the tokenization of heredoc/nowdoc closer tokens.
  *
  * @author    Juliette Reinders Folmer <phpcs_nospam@adviesenzo.nl>
  * @copyright 2020 Squiz Pty Ltd (ABN 77 084 670 600)
@@ -23,8 +23,8 @@ final class HeredocNowdocCloserTest extends AbstractMethodUnitTest
     /**
      * Verify that leading (indent) whitespace in a heredoc/nowdoc closer token get the tab replacement treatment.
      *
-     * @param string $testMarker The comment prefacing the target token.
-     * @param array  $expected   Expectations for the token array.
+     * @param string                         $testMarker The comment prefacing the target token.
+     * @param array<string, int|string|null> $expected   Expectations for the token array.
      *
      * @dataProvider dataHeredocNowdocCloserTabReplacement
      * @covers       PHP_CodeSniffer\Tokenizers\Tokenizer::createPositionMap
@@ -55,52 +55,52 @@ public function testHeredocNowdocCloserTabReplacement($testMarker, $expected)
      *
      * @see testHeredocNowdocCloserTabReplacement()
      *
-     * @return array
+     * @return array<string, array<string, string|array<string, int|string|null>>>
      */
     public static function dataHeredocNowdocCloserTabReplacement()
     {
         return [
-            [
+            'Heredoc closer without indent'      => [
                 'testMarker' => '/* testHeredocCloserNoIndent */',
                 'expected'   => [
                     'length'       => 3,
                     'content'      => 'EOD',
                     'orig_content' => null,
                 ],
             ],
-            [
+            'Nowdoc closer without indent'       => [
                 'testMarker' => '/* testNowdocCloserNoIndent */',
                 'expected'   => [
                     'length'       => 3,
                     'content'      => 'EOD',
                     'orig_content' => null,
                 ],
             ],
-            [
+            'Heredoc closer with indent, spaces' => [
                 'testMarker' => '/* testHeredocCloserSpaceIndent */',
                 'expected'   => [
                     'length'       => 7,
                     'content'      => '    END',
                     'orig_content' => null,
                 ],
             ],
-            [
+            'Nowdoc closer with indent, spaces'  => [
                 'testMarker' => '/* testNowdocCloserSpaceIndent */',
                 'expected'   => [
                     'length'       => 8,
                     'content'      => '     END',
                     'orig_content' => null,
                 ],
             ],
-            [
+            'Heredoc closer with indent, tabs'   => [
                 'testMarker' => '/* testHeredocCloserTabIndent */',
                 'expected'   => [
                     'length'       => 8,
                     'content'      => '     END',
                     'orig_content' => '	 END',
                 ],
             ],
-            [
+            'Nowdoc closer with indent, tabs'    => [
                 'testMarker' => '/* testNowdocCloserTabIndent */',
                 'expected'   => [
                     'length'       => 7,