Extract WindowManagerService test support logic.

This commit extracts the setup and teardown logic for
WindowManagerService tests from SystemServicesTestRule into a new file,
WindowManagerServiceTestSupport.kt. It allows other test modules to
reuse this logic.

Specifically, CarLaunchParamsModifierUpdatableTest, which directly calls
WindowManagerService.main, was missing the teardown logic updates in
SystemServicesTestRule causing test failures.

Bug: 356738240
Test: atest WmTests:WindowManagerServiceTests
Flag: com.android.window.flags.condense_configuration_change_for_simple_mode
Change-Id: I0ccccdfe39f366bcc0e247472034b07e2955368c