Correct SHOW_WALLPAPER conflicts the definition of isTranslucent

isTranslucent means this window may reveal apps behinds, so when a
window declared to show wallpaper, it must be opaque.

Bug: 236926198
Test: enable shell transition, open an app, press home and verify
there will play depth animation.

Change-Id: I0bed51de9155fe8ce1c00f1a838a4483b47dd515