Add test for markChapterCompleted in StateFragment [Blocked on #495]

[rt4914]

Once #495 is merged into develop, write test cases for Return to Topic functionality in app module code. This will be done later because in current develop test cases in player package are failing but updating those test cases is not a good idea as they are getting updating in #495 along with entire implementation change.

[rt4914]

This was finished in #495 . Reference:

oppia-android/app/src/sharedTest/java/org/oppia/android/app/player/state/StateFragmentTest.kt

Line 830 in 5fc69ff

fun testStateFragment_loadExp_continueToEndExploration_clickReturnToTopic_destroysActivity() {