Use ComposeViewAdapter for root in Window Manager

When the Window Manager is used in the Compose Preview, the base root
should be the ComposeViewAdapter. That ensures that the new 'windows'
created still obey the Compose Preview attributes like size.

Bug: 197931929
Test: checked from Studio
Change-Id: I07902b91475a89d5dc60927211483d40366abe52
(cherry picked from commit 318630bcaa42f694494592eb3b6328cda07640a8)
1 file changed