Update the freezer cutoff for aggressive freezing

Adding a flag to guard any further changes to support
more aggressive freezing.

Updating the freezer threshold to be lower when this flag is on. Further
lowering the threshold may not be possible without further changes to
keep important functionality working.

Flag: com.android.server.am.prototype_aggressive_freezing

Test: Manually check the value of the freezer cutoff when the flag is
enabled.

Bug: 370798593
Change-Id: I479145aaa7ab23852730e8c6f124829ab3dff8e8