[Wasm] Add Promise and support tests that return Promise

Co-authored-by: Ilya Gorbunov <Ilya.Gorbunov@jetbrains.com>

Merge-request: KT-MR-7717
Merged-by: Svyatoslav Kuzmich <svyatoslav.kuzmich@jetbrains.com>

libraries/stdlib/wasm/test/js/AsyncTest.kt

@@ -0,0 +1,63 @@
+package test.js
+
+import kotlin.js.*
+import kotlin.test.*
+
+@JsFun("async () => 'foo'")
+internal external fun jsAsyncFoo(): Promise<Dynamic?>
+
+@JsFun("() => 'foo'")
+internal external fun jsFoo(): Dynamic
+
+var state: Dynamic? = null
+
+class MyThrowable : Throwable()
+
+class AsyncTest {
+    @Test
+    fun test1(): Promise<Dynamic?> {
+        var thenExecuted = false
+        val p = jsAsyncFoo().then { value ->
+            state = value
+            thenExecuted = true
+            null
+        }
+        assertFalse(thenExecuted)
+        return p
+    }
+
+    @Test
+    fun test2(): Promise<Dynamic?> {
+        assertEquals(state, jsFoo())
+        var thenExecuted = false
+        val p = jsAsyncFoo().then {
+            assertEquals(state, jsFoo())
+            thenExecuted = true
+            null
+        }.then {
+            assertEquals(state, jsFoo())
+            thenExecuted = true
+            null
+        }
+        assertFalse(thenExecuted)
+        return p
+    }
+
+    @Test
+    fun testJsValueToThrowableOrNull1(): Promise<Dynamic?> {
+        val p = jsAsyncFoo().then {
+            throw MyThrowable()
+            null
+        }.catch { e ->
+            assert(e.toThrowableOrNull() is MyThrowable)
+            null
+        }
+        return p
+    }
+
+    @Test
+    fun testJsValueToThrowableOrNull2() {
+        val e = MyThrowable()
+        assertEquals((e as Dynamic).toThrowableOrNull(), e)
+    }
+}