Android Sunflower: update Kotlin to 1.2.20.
Android Sunflower: update Kotlin to 1.2.20.

Tracker: go/android-sunflower-tracker
PRD: go/android-sunflower-prd

Bug: 65952046
Test: ran unit and instrumented tests:
./gradlew app:test app:connectedAndroidTest

Change-Id: I095a4d364e9c1d481c2c9ba51a82034618bcc555

android/sunflower