refactor: remove static variables and add properties

To prevent inappropriate behavior when inheriting by using the values of the parent class on PHP 8.1.

Usage of static Variables in Inherited Methods
https://www.php.net/manual/en/migration81.incompatible.php

Author: kenjis

system/Database/BaseBuilder.php

@@ -244,6 +244,20 @@ class BaseBuilder
         'RIGHT OUTER',
     ];
 
+    /**
+     * Strings that determine if a string represents a literal value or a field name
+     *
+     * @var string[]
+     */
+    protected $isLiteralStr = [];
+
+    /**
+     * RegExp used to get operators
+     *
+     * @var string[]
+     */
+    protected $pregOperators = [];
+
     /**
      * Constructor
      *
@@ -2515,13 +2529,11 @@ protected function isLiteral(string $str): bool
             return true;
         }
 
-        static $_str;
-
-        if (empty($_str)) {
-            $_str = ($this->db->escapeChar !== '"') ? ['"', "'"] : ["'"];
+        if (empty($this->isLiteralStr)) {
+            $this->isLiteralStr = ($this->db->escapeChar !== '"') ? ['"', "'"] : ["'"];
         }
 
-        return in_array($str[0], $_str, true);
+        return in_array($str[0], $this->isLiteralStr, true);
     }
 
     /**
@@ -2610,11 +2622,9 @@ protected function hasOperator(string $str): bool
      */
     protected function getOperator(string $str, bool $list = false)
     {
-        static $_operators;
-
-        if (empty($_operators)) {
+        if (empty($this->pregOperators)) {
             $_les       = ($this->db->likeEscapeStr !== '') ? '\s+' . preg_quote(trim(sprintf($this->db->likeEscapeStr, $this->db->likeEscapeChar)), '/') : '';
-            $_operators = [
+            $this->pregOperators = [
                 '\s*(?:<|>|!)?=\s*', // =, <=, >=, !=
                 '\s*<>?\s*', // <, <>
                 '\s*>\s*', // >
@@ -2630,7 +2640,7 @@ protected function getOperator(string $str, bool $list = false)
             ];
         }
 
-        return preg_match_all('/' . implode('|', $_operators) . '/i', $str, $match) ? ($list ? $match[0] : $match[0][0]) : false;
+        return preg_match_all('/' . implode('|', $this->pregOperators) . '/i', $str, $match) ? ($list ? $match[0] : $match[0][0]) : false;
     }
 
     /**