Use Eagerly instead of WhileSubscribed for shortcuts

WhileSubscribed can be too slow, especially for shortcuts
that do work on background threads when the coroutine is
activated.

Fixes: 361789025
Test: manual - launch camera over lockscreen many times, observe
logs
Flag: EXEMPT bugfix

Change-Id: Ib48acf06830fae96381c3a150fd4952d5bfc1831