Change switches on resource IDs to if statements

Prepare for building the DocumentsUI code once as a library by using
if statements instead of switches on resource IDs.  Libraries are
compiled with non-final reosurce IDs, as the final IDs will be assigned
later during app linking.

Test: m DocumentsUI
Bug: 294256649
Change-Id: Ia48b0b35a891a6a427b67a7a09bfe6cab2663fc4