[benchs] add initial StringIterator benchmark

tests/benchs/src/cases/StringIterator.hx

@@ -0,0 +1,25 @@
+package cases;
+
+import hxbenchmark.Suite;
+import haxe.iterators.StringKeyValueIteratorUnicode;
+using StringTools;
+
+
+@:analyzer(no_local_dce)
+class StringIterator extends TestCase {
+	function measureL100() {
+		var s = "".lpad("a", 100);
+		var suite = new Suite("length 100");
+		suite.add("0...length + fastCodeAt",
+			for (key in 0...s.length) {
+				var value = s.fastCodeAt(key);
+			}
+		);
+		suite.add("StringKeyValueIteratorUnicode",
+			for (key => value in new StringKeyValueIteratorUnicode(s)) {
+
+			}
+		);
+		return suite.run();
+	}
+}