Use `kotlin-parcelize` plugin in buil.gradle

The `kotlin-parcelize` extension is available since Kotlin plugin 1.4.20 (https://kotlinlang.org/docs/whatsnew1420.html#kotlin-android-extensions), but we're currently on 1.4.10 to match the version used in WordPress for Android. 

We'll need to update it once the gradle plugin version gets updated too.