[JS IR] Add infra to test compilation with error

- add bunch of tests
 - fix help test

compiler/testData/codegen/boxError/semantic/missedBody.kt

@@ -0,0 +1,17 @@
+// ERROR_POLICY: SEMANTIC
+
+// FILE: t.kt
+
+fun bar(a: String, b: String): String
+
+fun foo(): String {
+    return bar("O", "K")
+}
+
+// FILE: b.kt
+
+fun box(): String {
+    val r = foo()
+    if (r is String) return r
+    return "OK"
+}