Android: Update Kotlin to 1.8.21

Additionally updates the serialization plugin to match

Source/Android/app/build.gradle

@@ -1,7 +1,7 @@
 plugins {
     id 'com.android.application'
     id 'org.jetbrains.kotlin.android'
-    id 'org.jetbrains.kotlin.plugin.serialization' version "1.7.20"
+    id 'org.jetbrains.kotlin.plugin.serialization' version "1.8.21"
 }
 
 task copyProfile (type: Copy) {