backend/tests: add tests for `==` with `Nothing`/`Nothing?`
backend/tests: add tests for `==` with `Nothing`/`Nothing?`

JetBrains/kotlin-native,JuliusKunze/kotlin-native,wiltonlazary/kotlin-native,JuliusKunze/kotlin-native,jiaminglu/kotlin-native,jiaminglu/kotlin-native,JetBrains/kotlin-native,JuliusKunze/kotlin-native,jiaminglu/kotlin-native,jiaminglu/kotlin-native,jiaminglu/kotlin-native,wiltonlazary/kotlin-native,JetBrains/kotlin-native,jiaminglu/kotlin-native,JetBrains/kotlin-native,JetBrains/kotlin-native,JetBrains/kotlin-native,JuliusKunze/kotlin-native,JetBrains/kotlin-native,JetBrains/kotlin-native,jiaminglu/kotlin-native,jiaminglu/kotlin-native,wiltonlazary/kotlin-native,JetBrains/kotlin-native,JuliusKunze/kotlin-native,JuliusKunze/kotlin-native,wiltonlazary/kotlin-native,wiltonlazary/kotlin-native,JuliusKunze/kotlin-native,JuliusKunze/kotlin-native