Modify rule S1781: add drupal conventions support (#4132)

rules/S1781/php/rule.adoc

@@ -6,6 +6,8 @@ This allows for more flexibility and ease of use when writing code.
 However, it is generally recommended to follow a consistent casing convention for readability and maintainability purposes.
 Relevant constants are `true`, `false` and `null`.
 
+Note that if the Drupal framework is detected, this rule will enforce Drupal standards instead.  Relevant constants are `TRUE`, `FALSE` and `NULL`.
+
 
 === Noncompliant code example
 
@@ -14,6 +16,13 @@ Relevant constants are `true`, `false` and `null`.
 <?php ECHO 'Hello World'; ?> 
 ----
 
+[source,php,diff-id=2,diff-type=noncompliant]
+----
+<?php
+// In a Drupal context
+const CACHE_ENABLED = true;
+?>
+----
 
 === Compliant solution
 
@@ -22,10 +31,20 @@ Relevant constants are `true`, `false` and `null`.
 <?php echo 'Hello World'; ?> 
 ----
 
+[source,php,diff-id=2,diff-type=compliant]
+----
+<?php
+// In a Drupal context
+const CACHE_ENABLED = TRUE;
+?>
+----
+
 == Resources
+
 === Documentation
-* https://www.php.net/manual/en/reserved.constants.php[PHP Manual - Predefined Constants]
 
+* https://www.php.net/manual/en/reserved.constants.php[PHP Manual - Predefined Constants]
+* https://www.drupal.org/docs/develop/standards/php/php-coding-standards#s-constants[Drupal - Naming Conventions - Constants]
 
 ifdef::env-github,rspecator-view[]