Convert FileManagementUiTest to Junit 4

There are 2 tests which were also failing due to the soft keyboard
failing to close. Updated to use the other methods so that it can
more reliably pass.

Bug: 407646510
Test: atest com.android.documentsui.FileManagementUiTest
Flag: EXEMPT test change
Change-Id: Ib9eb87d88f9d70ba6983b971259ba9e3d00c1db2