'async' reserved in front of function literals

compiler/testData/diagnostics/tests/ReservedAsync.kt

@@ -0,0 +1,21 @@
+fun async(f: () -> Unit) {
+    f()
+}
+
+infix fun Any.async(f: () -> Unit) = f()
+
+fun test(foo: Any) {
+    <!UNSUPPORTED!>async<!> {  }
+    <!UNSUPPORTED!>async<!> /**/ {  }
+    foo <!UNSUPPORTED!>async<!> {  }
+
+    async() { }
+
+    async({ })
+    foo async ({ })
+
+    foo <!UNSUPPORTED!>async<!> fun () {}
+    foo async (fun () {})
+
+    async (fun () {})
+}

compiler/testData/diagnostics/tests/ReservedAsync.txt

@@ -0,0 +1,5 @@
+package
+
+public fun async(/*0*/ f: () -> kotlin.Unit): kotlin.Unit
+public fun test(/*0*/ foo: kotlin.Any): kotlin.Unit
+public infix fun kotlin.Any.async(/*0*/ f: () -> kotlin.Unit): kotlin.Unit