[Wasm] Deprecate @JsFun with warning

kotlin.js.js("code") should be used instead

compiler/testData/diagnostics/wasmTests/jsInterop/jsFun.kt

@@ -1,3 +1,5 @@
+@file:Suppress("DEPRECATION")
+
 @JsFun("() => {}")
 external fun topLevelExternalFun(): Unit
 

libraries/stdlib/wasm/src/kotlin/JsInterop.kt

@@ -17,6 +17,7 @@ package kotlin
  *
  * This is a temporary annotation because K/Wasm <-> JS interop is not designed yet.
  */
+@Deprecated("@JsFun annotation is deprecated, use `fun f() = js(\"code\")` instead.")
 @Target(AnnotationTarget.FUNCTION, AnnotationTarget.PROPERTY_GETTER, AnnotationTarget.PROPERTY_SETTER)
 @Retention(AnnotationRetention.BINARY)
 public annotation class JsFun(val code: String)