Add a couple of php-cs-fixer clarifications and apply them

1. Disable the 'modernize_strpos' rule. It only can be applied
   to PHP >=8 and we still support 7.4. Pity that the rule itself,
   that is part of the Symfony ruleset is not able to act
   conditionally based on the PHP version.
2. We want the nullability chars (?) to be explicitly declared
   in parameters, no matter they are superfluous if the default
   is null. Way better than removing the default some day and
   forgetting to add them. Here the Symfony ruleset sucks.

Author: stronk7

.php-cs-fixer.php

@@ -15,6 +15,10 @@
     ->setRules([
         '@Symfony'                              => true,
         '@Symfony:risky'                        => true,
+        # Couple of changes from Symfony defaults
+        'modernize_strpos'                      => false, # TODO: Enable this once PHP8.0 is the min. req.
+        'nullable_type_declaration_for_default_null_value' => true, # We prefer explicit typing, no matter the defaults.
+        # We continue here.
         'array_syntax'                          => ['syntax' => 'short'],
         'combine_consecutive_unsets'            => true,
         'combine_consecutive_issets'            => true,

src/PluginValidate/Finder/AbstractParserFinder.php

@@ -32,7 +32,7 @@ abstract class AbstractParserFinder implements FinderInterface
      */
     protected $filter;
 
-    public function __construct(CodeParser $parser = null, StatementFilter $filter = null)
+    public function __construct(?CodeParser $parser = null, ?StatementFilter $filter = null)
     {
         $this->parser = $parser ?: new CodeParser();
         $this->filter = $filter ?: new StatementFilter();

src/Process/MoodleProcess.php

@@ -26,7 +26,7 @@ class MoodleProcess extends Process
      * @param array|null  $env     The environment variables or null to inherit
      * @param ?int        $timeout The timeout in seconds or null (default) to disable
      */
-    public function __construct(array $command, string $cwd = null, array $env = null, ?int $timeout = null)
+    public function __construct(array $command, ?string $cwd = null, ?array $env = null, ?int $timeout = null)
     {
         // Let's find our beloved php.
         $phpBinaryFinder = new PhpExecutableFinder();

tests/Fake/Process/DummyExecute.php

@@ -39,7 +39,7 @@ private function getMockProcess($cmd)
         return $process;
     }
 
-    public function run($cmd, string $error = null): Process
+    public function run($cmd, ?string $error = null): Process
     {
         if ($cmd instanceof Process) {
             // Get the command line from process.
@@ -49,7 +49,7 @@ public function run($cmd, string $error = null): Process
         return $this->helper->run($this->output, $this->getMockProcess($cmd), $error);
     }
 
-    public function mustRun($cmd, string $error = null): Process
+    public function mustRun($cmd, ?string $error = null): Process
     {
         if ($cmd instanceof Process) {
             // Get the command line from process.