[bc25] Fix clock centering logic on Dual Shade.

Since Dual Shade can be in either wide or narrow layout, relying on
ShadeMode to determine the clock centering is insufficient; the screen
width needs to be checked instead.

Flag: com.android.systemui.dual_shade
Flag: com.android.systemui.scene_container
Bug: 338033836
Bug: 352055453
Test: Added unit tests in ag/28236481, and they still pass.
Change-Id: I2bc5ae76d6d1dc8c5d4df9e1c23e3ade78e2af14