AC-6049: Filtering inputs handler in page_cache/block controller

         * allowing handles to start with numbers

Author: rizwankhgl

app/code/Magento/PageCache/Controller/Block.php

@@ -49,7 +49,7 @@ abstract class Block extends \Magento\Framework\App\Action\Action
     /**
      * Validation pattern for handles array
      */
-    private const VALIDATION_RULE_PATTERN = '/^[a-z]+[a-z0-9_]*$/i';
+    private const VALIDATION_RULE_PATTERN = '/^[a-z0-9]+[a-z0-9_]*$/i';
 
     /**
      * @param \Magento\Framework\App\Action\Context $context

app/code/Magento/PageCache/Test/Unit/Controller/Block/EsiTest.php

@@ -69,7 +69,7 @@ class EsiTest extends TestCase
     /**
      * Validation pattern for handles array
      */
-    private const VALIDATION_RULE_PATTERN = '/^[a-z]+[a-z0-9_]*$/i';
+    private const VALIDATION_RULE_PATTERN = '/^[a-z0-9]+[a-z0-9_]*$/i';
 
     /**
      * Set up before test

app/code/Magento/PageCache/Test/Unit/Controller/Block/RenderTest.php

@@ -74,7 +74,7 @@ class RenderTest extends TestCase
     /**
      * Validation pattern for handles array
      */
-    private const VALIDATION_RULE_PATTERN = '/^[a-z]+[a-z0-9_]*$/i';
+    private const VALIDATION_RULE_PATTERN = '/^[a-z0-9]+[a-z0-9_]*$/i';
 
     /**
      * @inheritDoc