IssueTracker

At the moment, types annotated with `@TypeConverter` must be instantiable. This prevents object expressions from being used as type converters. Since type converters are fairly likely to be pure functions adapting serialization/deserialization functions, it'd be useful if object expressions were supported.

The output generated by the Room processor for this input won't compile, because the generated Java tries to "new" the object expression type:

```kt
@Database(entities = [FooEntity::class], version = 1, exportSchema = false)
internal abstract class FooDatabase : RoomDatabase() {
  abstract fun fooDao(): FooDao
}

@Entity(tableName = "foo")
@TypeConverters(FooTypeConverters::class)
data class FooEntity internal constructor(
  @PrimaryKey val id: Int,

  val proto: SomeProto
)

object FooTypeConverters {
  @TypeConverter
  fun toSomeProto(bytes: ByteArray): SomeProto {
    return SomeProto.parseFrom(bytes)
  }

  @TypeConverter
  fun toBytes(someProto: SomeProto): ByteArray {
    return someProto.toByteArray()
  }
}
```