[DocsUI, Search]: Fix testEmptyQueryShowsDirectoryListing

Virtual keyboard can hide the directory. This CL adds closing of the
virtual keyboard, if visible.

Bug: 441152291
Flag: com.android.documentsui.flags.use_search_v2_read_only
Test: atest DocumentsUIGoogleTests
Change-Id: Id314acfb4621d73917bbb813983aedad6066d65b