[tests] Add test for static reflection on string

Author: tobil4sk

tests/unit/src/unit/issues/Issue12838.hx

@@ -0,0 +1,7 @@
+package unit.issues;
+
+class Issue12838 extends Test {
+	function test() {
+		eq(Reflect.callMethod(null, Reflect.field(String, "fromCharCode"), [65]), "A");
+	}
+}