Read Stem Primary Key Behaviors once in PhoneWindowManager#init

These behaviors were read as a configuration-dependent behaviors, every
time device configuration changed. Since the stem primary key is not
configuration dependent as of now, there's no need to re-read it on
every configuration change.

Bug: 283029769
Test: manual
Change-Id: I422a76743e1744a609710eea16ccac2232252edd