Add e2e for bringing desktop windows to front via the header

Launches a couple of apps and switches focus/front status between them
by tapping on their App Header.

Bug: 378909010
Flag: EXEMPT adding test
Test: atest PlatformScenarioTest:BringDesktopAppsToFrontTest
Change-Id: I4960f40b3e783ad0198f462f3f02c1ff8123ad28