Improve some sizeCompatMode Tests

Many of these tests bypass the whole hierarchy mechanism.
The purpose of the tests is to test the hierarchy behavior,
but they currently aren't very effective at catching
problems during hierarchy evaluation and are sensitive
to implementation details.

This changes the tests to manipulate the hierarchy via
its "interface" rather than manipulating full configuration
directly.

Bug: 138594779
Test: atest ActivityRecordTests
Change-Id: Ida70e8181558a1540fcce8fa8a188b6ceafaa27b