feat(phpstan): foundation for usage in extensions (#3666)

* feat(phpstan): pick up extended model relations typings
* feat(phpstan): pick up extended model date attributes
* feat(core): introduce `castAttribute` extender
Stops using `dates` as it's deprecated in laravel 8
* feat(phpstan): pick up extended model attributes through casts
* fix: extenders not resolved when declared namespace
* fix(phpstan): new model attributes are always nullable
* chore(phpstan): add helpful cache clearing command
* Apply fixes from StyleCI
* chore: improve extend files provider logic
* chore: rename `castAttribute` to just `cast`
* chore: update phpstan package to detect `cast` method
* Update framework/core/src/Extend/Model.php

Signed-off-by: Sami Mazouz <sychocouldy@gmail.com>

php-packages/phpstan/extension.neon

@@ -15,3 +15,27 @@ parameters:
     - stubs/Illuminate/Contracts/Filesystem/Factory.stub
     - stubs/Illuminate/Contracts/Filesystem/Cloud.stub
     - stubs/Illuminate/Contracts/Filesystem/Filesystem.stub
+
+services:
+	-
+		class: Flarum\PHPStan\Relations\ModelRelationsExtension
+		tags:
+			- phpstan.broker.methodsClassReflectionExtension
+			- phpstan.broker.propertiesClassReflectionExtension
+	-
+		class: Flarum\PHPStan\Attributes\ModelDateAttributesExtension
+		tags:
+			- phpstan.broker.propertiesClassReflectionExtension
+	-
+		class: Flarum\PHPStan\Attributes\ModelCastAttributeExtension
+		tags:
+			- phpstan.broker.propertiesClassReflectionExtension
+	-
+		class: Flarum\PHPStan\Extender\FilesProvider
+		arguments:
+			- %paths%
+	-
+		class: Flarum\PHPStan\Extender\Resolver
+		arguments:
+			- @Flarum\PHPStan\Extender\FilesProvider
+			- @defaultAnalysisParser