2x1 split-screen (2/n)

Handles an excption where creating a Toast object in the StageCoordinator constructor.

Bug: 439992109
Flag: com.android.wm.shell.enable_2x1_split
Test: Ensure no regression for existing Flex Split-Screen.
Change-Id: I0b2b1ac05693913c831575b11252937b4e0c2d28