[TASK] Use Declaration::getPropertyName() in RuleSet (#1519)

This method replaces `getRule()`, which is deprecated as of #1506.

Author: JakeQZ

CHANGELOG.md

@@ -35,7 +35,7 @@ Please also have a look at our
 - `Rule\Rule` class is deprecated; `Property\Declaration` is a direct
   replacement (#1508)
 - `Rule::setRule()` and `getRule()` are deprecated and replaced with
-  `setPropertyName()` and `getPropertyName()` (#1506)
+  `setPropertyName()` and `getPropertyName()` (#1506, #1519)
 
 ### Removed
 

src/RuleSet/RuleSet.php

@@ -101,7 +101,7 @@ public static function parseRuleSet(ParserState $parserState, RuleSet $ruleSet):
      */
     public function addRule(Declaration $declarationToAdd, ?Declaration $sibling = null): void
     {
-        $propertyName = $declarationToAdd->getRule();
+        $propertyName = $declarationToAdd->getPropertyName();
         if (!isset($this->declarations[$propertyName])) {
             $this->declarations[$propertyName] = [];
         }
@@ -240,7 +240,7 @@ public function getRulesAssoc(?string $searchPattern = null): array
         /** @var array<string, Declaration> $result */
         $result = [];
         foreach ($this->getRules($searchPattern) as $declaration) {
-            $result[$declaration->getRule()] = $declaration;
+            $result[$declaration->getPropertyName()] = $declaration;
         }
 
         return $result;
@@ -251,7 +251,7 @@ public function getRulesAssoc(?string $searchPattern = null): array
      */
     public function removeRule(Declaration $declarationToRemove): void
     {
-        $nameOfPropertyToRemove = $declarationToRemove->getRule();
+        $nameOfPropertyToRemove = $declarationToRemove->getPropertyName();
         if (!isset($this->declarations[$nameOfPropertyToRemove])) {
             return;
         }