Rename .java to .kt (viewmodel files)

This is an intermediate commit created by AndroidStudio while converting
java to kotlin, for preserving git history. Due to this CL, the next CL will show the
changes from Java to Kotlin code side by side.

Bug: 182205982
Test: None. File is renamed

Change-Id: Ife93b40880a3d7a9869704331ef7167baaff315d