DATACMNS-1197 - Resolve Kotlin interface properties for nullability inspection.

We now resolve Kotlin interface properties to inspect these for nullability. Kotlin-reflect does not resolve interface property accessors yet so we need to handle this aspect ourselves.

Related ticket: https://youtrack.jetbrains.com/issue/KT-20768.
Original pull request: #254.

src/test/kotlin/org/springframework/data/repository/core/support/KotlinUserRepository.kt

@@ -28,4 +28,6 @@ interface KotlinUserRepository : Repository<User, String> {
 	fun findById(username: String): User
 
 	fun findByOptionalId(username: String?): User?
+
+	val findRouteQuery: String
 }