Add flag to condense configuration changes.

In simple mode, display density, font size and navigation mode are
applied as preset settings, which trigger multiple configuration
changes. The new API introduced behind this flag condenses these
configuration changes to minimize frequent activity restarts.

Bug: 356738240
Test: Added a new flag only
Flag: com.android.window.flags.condense_configuration_change_for_simple_mode
Change-Id: I6a1925f37f93ae8483eff9fbda984fa73028565a