Support Kotlin in Robolectric test

Currently, Robolectric test written in Kotlin may not run, especially
when shards are in used, for example SettingsRoboTests has 10 shards.

This is because Robolectric test currently only recognize java files,
adding kt files to fix.

Rename current uniqueSrcFiles to uniqueJavaFiles, and compiledJavaSrcs
to uniqueSrcFiles. uniqueSrcFiles will contains both Java and Kotlin
files.

Note: android.FirstUniquePaths cannot be used, seems the behavior is
different and cause build error.

Bug: 252355400
Test: cd build/soong && mm
Test: m RunSettingsRoboTests with Kotlin tests
Change-Id: Id530ae4dcabffe01a06f44fe4234ffc67b73a601