feat: add polyfill for RegExp.escape

the method is currently in ECMAScript standard draft 4 and not yet adopted
broadly enough. V8 has basic support, but I'm not betting on it coming soon, so
I've implemented a simple polyfill.

src/polyfill/regexp.ts

@@ -0,0 +1,11 @@
+/**
+ * Polyfill for `RegExp.escape`, ensuring compatibility with environments
+ * that do not yet support this method.
+ *
+ * @see src/types/regexp.d.ts For the TypeScript type declaration.
+ */
+if (!RegExp.escape) {
+    RegExp.escape = function (str: string): string {
+        return str.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
+    };
+}

src/types/regexp.d.ts

@@ -0,0 +1,8 @@
+interface RegExpConstructor {
+    /**
+     * @see
+     * {@link https://tc39.es/proposal-regex-escaping/#sec-regexp.escape
+     * | ECMAScript Stage 4 Draft}
+     */
+    escape?(str: string): string;
+}

tsconfig.json

@@ -15,6 +15,7 @@
         "lib": ["esnext.weakref", "dom"]
     },
     "include": [
-        "src/**/*.ts"
+        "src/**/*.ts",
+        "src/types/**/*.d.ts"
     ]
 }