Use desktop corner radius for initial task snapshot

When converting a task to bubble, we initially show a snapshot of the
task before starting the animation to bubble.
Use the desktop drag corner radius for the initial snapshot corner
radius so it matches the dragged task.

Bug: 396449031
Test: atest BubbleTransitionsTest
Test: manual, drag a task to bubble
Flag: com.android.wm.shell.enable_bubble_to_fullscreen
Change-Id: I766c3aac7101e1ddbfb743dc3ed86efb7d8b6c16