Make max notification icon values resources instead of hard-coded vals.

This will allow us to customize these values based on device type/screen
orientation/size etc as needed.

Bug: 254068247
Test: atest NotificationIconContainerTest
Test: manually verified that nothing is changed in the behavior of the
icon container

Change-Id: I304b623e5c15c947cd2ddfe6b5fe977cbadd0e54