Fix a few UI issues based around multiselect in new nav.

 - No longer crashes when entering mw-mode while in multiselect
 - Configuration changes now properly restore bottom nav visibility
 - toolbar shadow is now only visible in search

Bug: 72525324
Test: MainActivityOldPeerSearchIntegrationTest
PiperOrigin-RevId: 186037379
Change-Id: I5fc00c8091e85fc67482b2131944fb776626d06f