Allow using big CPU cores during a user switch.

This CL allows system server and system ui processes to use all of the
CPU cores during a user switch. This improves core user switch
duration (without the dialog animations) by 20%, and the standard
deviation by 35%.

Bug: 308106771
Flag: ACONFIG android.multiuser.allow_using_all_cpu_cores_during_a_user_switch DEVELOPMENT
Test: Perfetto trace
Change-Id: I51c998c9dd5d8a6af5871741f4b0e9ab5b4f8f92