Add a crash handler to run on Init

This CL introduces a new crash handler class to be run when the shell
processs is being initialized. Also refactors some of the shared logic
for launching home intent into its seperate class.

Fix: 396661883
Test: Manually crash sysui and observe that user ends up in home screen
Test: atest ShellCrashHandlerTest
Flag: EXEMPT Bug fix
Change-Id: I7d51119c389a18d03bf0cb3c3204ee434c062c18