Retain the last merged config to the requested override config for PiP.

Avoid propagating config changes for CONFIG_TOUCHSCREEN,
CONFIG_COLORMODE and CONFIG_DENSITY since apps are known to be destroyed
and restarted on these config changes and they affect PiP quality on
transferring PiP across displays.

Test: atest ActivityRecordTests
Flag: com.android.window.flags.enable_dragging_pip_across_displays
Fixes: 422565128
Change-Id: I824ab315dbefd2b9a2a5d4ffc7b930586aba1b73