Add config changes consolidation to SettingsLib.

This commit adds a new API to DisplayDensityConfiguration that allows
setting the display density within the context of a batch update.

SimpleModeUtils now calls the new method to consolidate configuration
updates for display size, font size and navigation mode in ag/30875650.

Bug: 356738240
Test: adb shell am start -a com.google.android.settings.matcha.ACCESSIBILITY_APPEARANCE_SETTINGS -c android.intent.category.DEFAULT
Test: adb shell am start -n com.android.settings/com.google.android.settings.simplemode.SimpleModeSettingsActivity
Flag: com.android.window.flags.condense_configuration_change_for_simple_mode
Change-Id: Ia6fd575fc47f73d9c8862b9ddfcb74ca14ce7599