Disallow too large display padding for wallpaper

To avoid a potential vulnerability, don't allow padding
with width or height larger than the maximum screen width.

Bug: 204316511
Test: added WallpaperManagerTest
Change-Id: I471fb3546bdd2f9aa07dd091fe841b2bc5c484d6
Merged-In: I471fb3546bdd2f9aa07dd091fe841b2bc5c484d6