DocsUI: Add VersionUtils to proguard config

This util is intended to use across different Android versions and
should not be stripped out and it's just small utility functions.

Bug: 442400425
Test: atest DocumentsUIGoogleTests:com.android.documentsui.services.TrashJobTest
Flag: com.android.documentsui.flags.enable_trash_flow_ro
Change-Id: I9c64af76ca2bd4db59c50b57272b02d81494c22f