Compress singlecode for ldStringByIndex

Issue: https://gitee.com/openharmony/arkcompiler_ets_runtime/issues/IACQOS?from=project-issue
Signed-off-by: 刘智杰 <liuzhijie9@huawei.com>
Change-Id: I59be68a5dfc2e9bb5ecd06b2c9b631b86d8b1e5c

ecmascript/compiler/builtins/builtins_string_stub_builder.cpp

@@ -1190,7 +1190,9 @@ GateRef BuiltinsStringStubBuilder::CreateStringBySingleCharCode(GateRef glue, Ga
     BRANCH(canStoreAsUtf8, &utf8, &utf16);
     Bind(&utf8);
     {
-        newBuilder.AllocLineStringObject(&result, &afterNew, Int32(1), true);
+        GateRef singleCharTable = GetSingleCharTable(glue);
+        result = GetValueFromTaggedArray(singleCharTable, charCode);
+        Jump(&exit);
     }
     Bind(&utf16);
     {

test/aottest/ldobjbyvalue/ldobjbyvalue.ts

@@ -38,3 +38,40 @@ function testHolyArray() {
     print(arrayTest[9] === undefined);
 }
 testHolyArray();
+
+function testStringIndex() {
+    class A {
+        constructor() {
+            var gotoFn = {
+                0: {}
+            };
+        
+            this.gotoFn = gotoFn;
+        }
+        
+        search(string) {
+            var state = 0;
+            var results = [];
+            for (var i=0; i<string.length; i++) {
+                var l = string[i];
+                if (!(l in this.gotoFn[state])) {
+                    continue;
+                }
+                state = this.gotoFn[state][l];
+            }
+        
+            return results;
+        };
+    }
+
+
+    let words = ""
+    for (let i = 0; i < 100; i++) {
+        words += "should find keyword" + i + " at position " + i + "and"
+    }
+    let ac = new A();
+    for (let i = 0; i < 100; i++) {
+        ac.search(words)
+    }
+}
+testStringIndex();