Override WindowManagerImpl from the platform

Layoutlib replaces the platform implementation of
android.view.WindowManagerImpl, and this implementation
does not support multi-window.

Bug: 157542546
Test: N/A
Change-Id: I84db355aa6da28e7cc2d30e6df83f1f397aa9561
(cherry picked from commit a70908fb1e4ed30c075ed5cb1facc3710d67216d)
3 files changed