Support turning off @internal check (#754)

* Support turning off @internal check

fixes #747

* Add README.md changes

Author: mglaman

README.md

@@ -91,6 +91,19 @@ See the `extension-installer` documentation for more information: https://github
 
 ## Adapting to your project
 
+### Customizing rules
+
+#### Disabling checks for extending `@internal` classes
+
+You can disable the `ClassExtendsInternalClassRule` rule by adding the following to your `phpstan.neon`:
+
+```neon
+parameters: 
+    drupal:
+        rules:
+            classExtendsInternalClassRule: false
+```
+
 ### Specifying your Drupal project's root
 
 By default, the PHPStan Drupal extension will try to determine your Drupal project's root directory based on the working

extension.neon

@@ -23,6 +23,7 @@ parameters:
 			testClassSuffixNameRule: false
 			dependencySerializationTraitPropertyRule: false
 			accessResultConditionRule: false
+			classExtendsInternalClassRule: true
 		entityMapping:
 			aggregator_feed:
 				class: Drupal\aggregator\Entity\Feed
@@ -246,6 +247,7 @@ parametersSchema:
 			testClassSuffixNameRule: boolean()
 			dependencySerializationTraitPropertyRule: boolean()
 			accessResultConditionRule: boolean()
+			classExtendsInternalClassRule: boolean()
 		])
 		entityMapping: arrayOf(anyOf(
 			structure([

rules.neon

@@ -3,7 +3,6 @@ rules:
 	- mglaman\PHPStanDrupal\Rules\Drupal\GlobalDrupalDependencyInjectionRule
 	- mglaman\PHPStanDrupal\Rules\Drupal\PluginManager\PluginManagerSetsCacheBackendRule
 	- mglaman\PHPStanDrupal\Rules\Deprecations\AccessDeprecatedConstant
-	- mglaman\PHPStanDrupal\Rules\Classes\ClassExtendsInternalClassRule
 	- mglaman\PHPStanDrupal\Rules\Classes\PluginManagerInspectionRule
 	- mglaman\PHPStanDrupal\Rules\Deprecations\ConditionManagerCreateInstanceContextConfigurationRule
 	- mglaman\PHPStanDrupal\Rules\Drupal\RenderCallbackRule
@@ -27,6 +26,8 @@ conditionalTags:
 		phpstan.rules.rule: %drupal.rules.dependencySerializationTraitPropertyRule%
 	mglaman\PHPStanDrupal\Rules\Drupal\AccessResultConditionRule:
 		phpstan.rules.rule: %drupal.rules.accessResultConditionRule%
+	mglaman\PHPStanDrupal\Rules\Classes\ClassExtendsInternalClassRule:
+		phpstan.rules.rule: %drupal.rules.classExtendsInternalClassRule%
 
 services:
 	-
@@ -37,3 +38,5 @@ services:
 		class: mglaman\PHPStanDrupal\Rules\Drupal\AccessResultConditionRule
 		arguments:
 			treatPhpDocTypesAsCertain: %treatPhpDocTypesAsCertain%
+	-
+		class: mglaman\PHPStanDrupal\Rules\Classes\ClassExtendsInternalClassRule