[KAPT] Warn about usage of types from default package

Java doesn't support import from default package. 
We can't fix it, so we warn about it.
#KT-36743

plugins/kapt3/kapt3-compiler/testData/converter/defaultPackage.kt

@@ -0,0 +1,45 @@
+// STRICT
+
+//FILE: test/ClassRefAnnotation.java
+
+package test;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+import java.lang.annotation.ElementType;
+
+@Target({ ElementType.TYPE, ElementType.METHOD })
+@Retention(RetentionPolicy.RUNTIME)
+public @interface ClassRefAnnotation {
+    Class<?>[] value();
+}
+
+//FILE: a.kt
+
+class RootClass
+
+class AnotherRootClass
+
+//FILE: b.kt
+package test
+
+import java.lang.Number as JavaNumber
+import RootClass
+import AnotherRootClass as Arc
+
+interface PackedClass {
+    fun someMethod(): RootClass
+    fun otherMethod(): JavaNumber
+    fun oneMoreMethod(): Arc
+}
+
+@ClassRefAnnotation(RootClass::class)
+class PackedWithAnnotation
+
+// EXPECTED_ERROR(kotlin:11:5) cannot find symbol
+// EXPECTED_ERROR(kotlin:14:1) cannot find symbol
+// EXPECTED_ERROR(kotlin:9:5) cannot find symbol
+// EXPECTED_ERROR(other:-1:-1) test.PackedClass: Can't reference type 'RootClass' from default package in Java stub.
+// EXPECTED_ERROR(other:-1:-1) test.PackedClass: Can't reference type 'AnotherRootClass' from default package in Java stub.
+// EXPECTED_ERROR(other:-1:-1) test.PackedWithAnnotation: Can't reference type 'RootClass' from default package in Java stub.