Update coding style to include PSR-12, among other options

This also includes heavy use of slevomat/coding-standard to apply
various checks to the code, based on maintainer (me) preference.

tests/phpstan-bootstrap.php

@@ -1,5 +1,11 @@
 <?php
 
+/**
+ * PHPStan bootstrap
+ *
+ * @codingStandardsIgnoreFile
+ */
+
 if (!function_exists('uuid_create')) {
     /**
      * @param int $type