[CLEANUP] rector: Add strict return type based on returned strict exp…

…r type

This applies the rule ReturnTypeFromStrictBoolReturnExprRector. For
Details see:
https://github.com/rectorphp/rector/blob/main/docs/rector_rules_overview.md#returntypefromstrictboolreturnexprrector

Signed-off-by: Daniel Ziegenberg <daniel@ziegenberg.at>

src/CSSList/AtRuleBlockList.php

@@ -77,7 +77,7 @@ public function render(OutputFormat $oOutputFormat)
     /**
      * @return bool
      */
-    public function isRootList()
+    public function isRootList(): bool
     {
         return false;
     }

src/CSSList/Document.php

@@ -166,7 +166,7 @@ public function render(OutputFormat $oOutputFormat = null)
     /**
      * @return bool
      */
-    public function isRootList()
+    public function isRootList(): bool
     {
         return true;
     }

src/CSSList/KeyFrame.php

@@ -82,7 +82,7 @@ public function render(OutputFormat $oOutputFormat)
     /**
      * @return bool
      */
-    public function isRootList()
+    public function isRootList(): bool
     {
         return false;
     }

src/Parsing/ParserState.php

@@ -430,7 +430,7 @@ private function inputLeft()
      *
      * @return bool
      */
-    public function streql($sString1, $sString2, $bCaseInsensitive = true)
+    public function streql($sString1, $sString2, $bCaseInsensitive = true): bool
     {
         if ($bCaseInsensitive) {
             return $this->strtolower($sString1) === $this->strtolower($sString2);

src/RuleSet/DeclarationBlock.php

@@ -132,7 +132,7 @@ public function setSelectors($mSelector, $oList = null)
      *
      * @return bool
      */
-    public function removeSelector($mSelector)
+    public function removeSelector($mSelector): bool
     {
         if ($mSelector instanceof Selector) {
             $mSelector = $mSelector->getSelector();

src/Value/Size.php

@@ -190,7 +190,7 @@ public function isSize()
     /**
      * @return bool
      */
-    public function isRelative()
+    public function isRelative(): bool
     {
         if (in_array($this->sUnit, self::RELATIVE_SIZE_UNITS, true)) {
             return true;