[CLEANUP] Rector: Change numeric return type based on strict returns type operations (#586)

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

Signed-off-by: Daniel Ziegenberg <[email protected]>

Author: ziegenberg

src/Parsing/ParserState.php

@@ -449,10 +449,8 @@ public function backtrack($iAmount)
 
     /**
      * @param string $sString
-     *
-     * @return int
      */
-    public function strlen($sString)
+    public function strlen($sString): int
     {
         if ($this->oParserSettings->bMultibyteSupport) {
             return mb_strlen($sString, $this->sCharset);