[Wasm] Add @JsExport diagnostics test

@JsExport is only allowed on top-level functions in K/Wasm

Restrictions for nested function are handled by reusing K/JS diagnostics
Restrictions for classes and properties are handled by specifying
 annotation target in stdlib

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

@@ -0,0 +1,25 @@
+// !OPT_IN: kotlin.js.ExperimentalJsExport
+
+@JsExport
+fun foo1() {
+}
+
+class C {
+    <!NESTED_JS_EXPORT!>@JsExport<!>
+    fun memberFunction() {
+    }
+}
+
+fun foo2() {
+    <!NESTED_JS_EXPORT!>@JsExport<!>
+    fun localFun() {
+    }
+}
+
+val p1 = (<!NESTED_JS_EXPORT!>@JsExport<!> fun () {})
+
+<!WRONG_ANNOTATION_TARGET!>@JsExport<!>
+class C2
+
+<!WRONG_ANNOTATION_TARGET!>@JsExport<!>
+var p2: Int = 1

wasm/wasm.tests/tests-gen/org/jetbrains/kotlin/wasm/test/diagnostics/DiagnosticsWasmTestGenerated.java

@@ -50,5 +50,11 @@ public class DiagnosticsWasmTestGenerated extends AbstractDiagnosticsWasmTest {
         public void testInheritance() throws Exception {
             runTest("compiler/testData/diagnostics/wasmTests/jsInterop/inheritance.kt");
         }
+
+        @Test
+        @TestMetadata("jsExport.kt")
+        public void testJsExport() throws Exception {
+            runTest("compiler/testData/diagnostics/wasmTests/jsInterop/jsExport.kt");
+        }
     }
 }