JS: fixed subSequence in CharSequence descendants (KT-14035) + added support for function intrics in delegation

js/js.translator/testData/box/expression/stringClass/subSequence.kt

@@ -1,5 +1,15 @@
 package foo
 
+class CC(val s: CharSequence) : CharSequence by s, MyCharSequence {}
+
+interface MyCharSequence {
+    val length: Int
+
+    operator fun get(index: Int): Char
+
+    fun subSequence(startIndex: Int, endIndex: Int): CharSequence
+}
+
 fun box(): String {
     val kotlin: String = "kotlin"
 
@@ -11,5 +21,20 @@ fun box(): String {
     val tlin = (kotlin as CharSequence).subSequence(2, 6)
     if (tlin.toString() != "tlin") return "Fail 2: $tlin"
 
+    val cc: CharSequence = CC(kotlin)
+    if (cc.length != 6) return "Fail 3: ${cc.length}"
+    if (cc.subSequence(0, 3) != kot) return "Fail 4"
+    if (cc[2] != 't') return "Fail 5: ${cc[2]}"
+
+    val mcc: MyCharSequence = CC(kotlin)
+    if (mcc.length != 6) return "Fail 6: ${mcc.length}"
+    if (mcc.subSequence(0, 3) != kot) return "Fail 7"
+    if (mcc[2] != 't') return "Fail 8: ${mcc[2]}"
+
+    val ccc = CC(cc)
+    if (ccc.length != 6) return "Fail 6: ${ccc.length}"
+    if (ccc.subSequence(0, 3) != kot) return "Fail 7"
+    if (ccc[2] != 't') return "Fail 8: ${ccc[2]}"
+
     return "OK"
 }