Add touch filtering for Top Intro Preference

- Adds touch filtering for the Top Intro Preference. This makes
the preference not clickable when it's obscured by other windows.

HIGH_LEVEL_CL_EXPLANATION:
- Tapjacking is currently possible on the TopIntroPreference. Set android:filterTouchesWhenObscured to true to mitigate. (See: https://developer.android.com/privacy-and-security/risks/tapjacking)

Bug: 391457154 
Change-Id: I7bcb72d9387d2ad88eb34c0c8cbca8f48bd6537d
Flag: EXEMPT library
Test: atest & manual