Add screen size parameterization to `TestRunner`.

Introduce `@ParameterizeScreenSizes` annotation and `ScreenSize` enum to
run tests across different window sizes. The `TestRunner` now generates
test instances for each combination of flag overrides and specified
screen sizes, using `wm size` commands to adjust the display size before
each test run. Screen size parameterization is only enabled on devices
supporting freeform window management.

Bug: 438342600
Flag: EXEMPT changing tests
Test: Changing tests
Change-Id: Ida6c1497fb28703d2993549a4c5ca94c6b75b246