[Wasm] Migrate usages of @JsFun to js("code")

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

@@ -3,11 +3,11 @@ package test.js
 import kotlin.js.*
 import kotlin.test.*
 
-@JsFun("async () => 'foo'")
-internal external fun jsAsyncFoo(): Promise<Dynamic?>
+internal fun jsAsyncFoo(): Promise<Dynamic?> =
+    js("(async () => 'foo')()")
 
-@JsFun("() => 'foo'")
-internal external fun jsFoo(): Dynamic
+internal fun jsFoo(): Dynamic =
+    js("'foo'")
 
 var state: Dynamic? = null
 

libraries/stdlib/wasm/test/unsafe/MemoryAllocationTest.kt

@@ -3,8 +3,8 @@ package test.wasm.unsafe
 import kotlin.wasm.unsafe.*
 import kotlin.test.*
 
-@JsFun("(a, b) => a + b")
-private external fun jsConcatStrings(a: String, b: String): String
+private fun jsConcatStrings(a: String, b: String): String =
+    js("a + b")
 
 @OptIn(UnsafeWasmMemoryApi::class)
 class MemoryAllocationTest {