JS: initialize fields of coroutine state machine with undefined value so that they match local variable semantics. Fix KT-15366

compiler/testData/codegen/box/coroutines/multiModule/inlineFunctionWithOptionalParam.kt

@@ -0,0 +1,30 @@
+// MODULE: lib
+// FILE: lib.kt
+inline fun foo(x: String = "OK"): String {
+    return x + x
+}
+
+// MODULE: main(lib)
+// FILE: main.kt
+// WITH_RUNTIME
+// WITH_COROUTINES
+import kotlin.coroutines.*
+
+var result = ""
+
+fun builder(c: suspend () -> Unit) {
+    c.startCoroutine(object : Continuation<Unit> {
+        override fun resume(value: Unit) {
+        }
+        override fun resumeWithException(exception: Throwable) {
+        }
+    })
+}
+
+fun box(): String {
+    builder {
+        result = foo()
+    }
+    if (result != "OKOK") return "fail: $result"
+    return "OK"
+}