Kotlin 1.9.0 (#3835)

Update to Kotlin 1.9.0 and migrate to newer language idioms.

- Remove unnecessary @OptIn for features migrated to mainstream
- Use `data object` where appropriate
- Use new enum `entries` property

app/src/main/java/com/keylesspalace/tusky/db/AccountEntity.kt

@@ -129,9 +129,7 @@ data class AccountEntity(
         other as AccountEntity
 
         if (id == other.id) return true
-        if (domain == other.domain && accountId == other.accountId) return true
-
-        return false
+        return domain == other.domain && accountId == other.accountId
     }
 
     override fun hashCode(): Int {