FIR LC: fix nullable annotation on return type of suspend function

compiler/testData/asJava/ultraLightClasses/coroutines.java

@@ -7,6 +7,8 @@ public final class Foo /* Foo*/ {
 }
 
 public final class Boo /* Boo*/ {
+  private final java.lang.Object doSomething(Foo, kotlin.coroutines.Continuation<? super Bar>);//  doSomething(Foo, kotlin.coroutines.Continuation<? super Bar>)
+
   public  Boo();//  .ctor()
 
 }
@@ -30,4 +32,4 @@ public final class Derived /* Derived*/ implements Base {
 
   public  Derived();//  .ctor()
 
-}
+}

compiler/testData/asJava/ultraLightClasses/coroutines.kt

@@ -1,4 +1,5 @@
 //RELEASE_COROUTINE_NEEDED
+//CHECK_BY_JAVA_FILE
 class Foo {
   suspend fun doSomething(foo: Foo): Bar {}
 }
@@ -18,3 +19,5 @@ interface Base {
 class Derived: Base {
     override suspend fun foo() { ... }
 }
+
+// FIR_COMPARISON

compiler/testData/asJava/ultraLightFacades/coroutines.kt

@@ -1,4 +1,6 @@
 //RELEASE_COROUTINE_NEEDED
 suspend fun doSomething(foo: String): Int {}
 
-fun <T> async(block: suspend () -> T)
+fun <T> async(block: suspend () -> T)
+
+// FIR_COMPARISON