Tests/BackfillExplicitOctalNotationTest: 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.

Author: jrfnl

tests/Core/Tokenizer/BackfillExplicitOctalNotationTest.php

@@ -47,66 +47,66 @@ public function testExplicitOctalNotation($marker, $value, $nextToken, $nextCont
      *
      * @see testExplicitOctalNotation()
      *
-     * @return array
+     * @return array<string, array<string, int|string>>
      */
     public static function dataExplicitOctalNotation()
     {
         return [
-            [
+            'Explicit octal'                                                                                       => [
                 'marker'      => '/* testExplicitOctal */',
                 'value'       => '0o137041',
                 'nextToken'   => T_SEMICOLON,
                 'nextContent' => ';',
             ],
-            [
+            'Explicit octal - capitalized O'                                                                       => [
                 'marker'      => '/* testExplicitOctalCapitalised */',
                 'value'       => '0O137041',
                 'nextToken'   => T_SEMICOLON,
                 'nextContent' => ';',
             ],
-            [
+            'Explicit octal - with numeric literal separator'                                                      => [
                 'marker'      => '/* testExplicitOctalWithNumericSeparator */',
                 'value'       => '0o137_041',
                 'nextToken'   => T_SEMICOLON,
                 'nextContent' => ';',
             ],
-            [
+            'Invalid explicit octal - numeric literal separator directly after "0o"'                               => [
                 'marker'      => '/* testInvalid1 */',
                 'value'       => '0',
                 'nextToken'   => T_STRING,
                 'nextContent' => 'o_137',
             ],
-            [
+            'Invalid explicit octal - numeric literal separator directly after "0O" (capitalized O)'               => [
                 'marker'      => '/* testInvalid2 */',
                 'value'       => '0',
                 'nextToken'   => T_STRING,
                 'nextContent' => 'O_41',
             ],
-            [
+            'Invalid explicit octal - number out of octal range'                                                   => [
                 'marker'      => '/* testInvalid3 */',
                 'value'       => '0',
                 'nextToken'   => T_STRING,
                 'nextContent' => 'o91',
             ],
-            [
+            'Invalid explicit octal - part of the number out of octal range'                                       => [
                 'marker'      => '/* testInvalid4 */',
                 'value'       => '0O2',
                 'nextToken'   => T_LNUMBER,
                 'nextContent' => '82',
             ],
-            [
+            'Invalid explicit octal - part of the number out of octal range with numeric literal separator after'  => [
                 'marker'      => '/* testInvalid5 */',
                 'value'       => '0o2',
                 'nextToken'   => T_LNUMBER,
                 'nextContent' => '8_2',
             ],
-            [
+            'Invalid explicit octal - part of the number out of octal range with numeric literal separator before' => [
                 'marker'      => '/* testInvalid6 */',
                 'value'       => '0o2',
                 'nextToken'   => T_STRING,
                 'nextContent' => '_82',
             ],
-            [
+            'Invalid explicit octal - explicit notation without number'                                            => [
                 'marker'      => '/* testInvalid7 */',
                 'value'       => '0',
                 'nextToken'   => T_STRING,