Adds flag for opening WPP directly from keyguard long-press.

If this flags is enabled, the long-press lock screen gesture will
directly open the wallpaper picker lock screen settings tab, skipping
the popup.

Bug: 275517886
Test: Tested with the next CL in the chain.
Change-Id: Id41e82b903d19c4e58778f0dcb22a45c83b0a388