Add custom site map pairs into SettingsSearchIndexablesProvider

Settings Search need Settings to provide custom site map pairs to build
up full breadcrumb for the search results from ScreenLockSettings,
WallpaperSuggestionActivity and WifiSettings2.

Bug: 147851992
Bug: 151206664
Test: manual test with Settings Search, robotests
Change-Id: Ide6e69b3336af255a388737d46147f2fc2ef9790